JP7636695B2 - Method for producing aqueous fluorine-containing elastomer dispersion - Google Patents

Description

The present disclosure relates to a method for producing an aqueous dispersion of a fluorine-containing elastomer.

As a method for producing an aqueous dispersion of a fluorine-containing elastomer, Patent Document 1 describes emulsion polymerization using a reactive surfactant consisting of a compound having a radically polymerizable unsaturated bond and a hydrophilic group in the molecule.

JP 2007-045970 A

The present disclosure aims to provide a manufacturing method that can smoothly polymerize a fluorine-containing monomer while suppressing adhesion of the fluorine-containing elastomer to the polymerization tank, without using a relatively large amount of reactive surfactant as in conventional manufacturing methods.

According to the present disclosure, there is provided a method for producing an aqueous fluorine-containing elastomer dispersion, which comprises polymerizing a fluorine-containing monomer in the presence of an aqueous medium and a fluorine-containing compound (A) to produce an aqueous dispersion containing a fluorine-containing elastomer, the fluorine-containing elastomer comprising a methylene group in its main chain, and a fluorine-containing compound (A) represented by the general formula (A):
CX ⁱ X ^k =CX ^j R ^a -(CZ ¹ Z ² ) _k -Y ³ (A)
⁽ wherein Xi, ^Xj and ^Xk are the same or different and are F, Cl, H or _CF3 ; ^Y3 is a hydrophilic group; R ^a is a linking group; ^Z1 and ^Z2 are the same or different and are H, F or _CF3 ; k is 0 or 1, with the proviso that at least one of Xi, ^Xk , ^Xj , ^{R a} , ^Z1 and ^Z2 contains F. The number of carbon atoms in the portion excluding the hydrophilic group is 6 or less), and a production method is provided which comprises initiating polymerization of the fluorine-containing monomer and then supplying a fluorine-containing compound (A).

The hydrophilic group is preferably _-NH2 , -P(O)(OM) ₂ , -OP(O)(OM) ₂ , _-SO3M , _-OSO3M or -COOM (in each formula, M is _H , a metal atom, ^NR74 , imidazolium which may have a substituent, pyridinium which may have a substituent or phosphonium which may have a substituent, ^R7 is H or an organic group and may be the same or different, and any two of them may be bonded to each other to form a ring).
The fluorine-containing elastomer preferably contains a vinylidene fluoride unit.
The fluorine-containing elastomer preferably contains vinylidene fluoride units in an amount of 50 mol % or more based on the total monomer units.
It is preferable to supply the fluorine-containing compound (A) also before the initiation of polymerization of the fluorine-containing monomer.
The amount of the fluorine-containing compound (A) supplied after the initiation of polymerization of the fluorine-containing monomer is preferably 30 to 300 ppm by mass relative to the aqueous medium.
It is preferable to polymerize the fluorine-containing monomer in the absence of a fluorine-containing surfactant having substantially no radically polymerizable unsaturated bond.
The fluorine-containing elastomer preferably has a Mooney viscosity (ML1+10 (100° C.)) of 10 to 130.
The fluorine-containing compound (A) is represented by the general formula (A1):
CX ⁱ X ^k =CX ^j -OR-(CZ ¹ Z ² ) _k -Y ³
(wherein Xi, ^Xj , ^Xk , ^Z1 , ^Z2 , k ^{and Y3} are as defined above, and R is a fluorinated alkylene group or a fluorinated oxyalkylene group having 1 to 3 carbon atoms), and a compound represented by general formula (A2):
CX ⁱ X ^k =CX ^j -CZ ¹ Z ² -O-R-(CZ ¹ Z ² ) _k -Y ^3
( wherein Xi, ^Xj , ^Xk , ^Z1 , ^Z2 , k and ^Y3 are as defined above, and R is a fluorinated alkylene group or a fluorinated oxyalkylene group having 1 or 2 carbon atoms).

According to the present disclosure, a manufacturing method can be provided that can smoothly polymerize a fluorine-containing monomer while suppressing adhesion of the fluorine-containing elastomer to the polymerization tank, without using a relatively large amount of reactive surfactant as in conventional manufacturing methods.

Before describing specific embodiments of the present disclosure, we will define or explain some terms used in the present disclosure.

In this disclosure, a fluoroelastomer is an amorphous fluoropolymer. "Amorphous" refers to a fluoropolymer whose melting peak (ΔH) in differential scanning calorimetry (DSC) (heating rate 10°C/min) or differential thermal analysis (DTA) (heating rate 10°C/min) is 4.5 J/g or less. Fluorine-containing elastomers exhibit elastomeric properties by crosslinking. Elastomeric properties refer to the ability of a polymer to be stretched and to retain its original length when the force required to stretch the polymer is no longer applied.

In this disclosure, a perfluoromonomer is a monomer that does not contain a carbon atom-hydrogen atom bond in the molecule. The perfluoromonomer may be a monomer in which some of the fluorine atoms bonded to the carbon atom are replaced with chlorine atoms, in addition to carbon atoms and fluorine atoms, and may also have nitrogen atoms, oxygen atoms, sulfur atoms, phosphorus atoms, boron atoms, or silicon atoms in addition to carbon atoms. The perfluoromonomer is preferably a monomer in which all hydrogen atoms are replaced with fluorine atoms. The perfluoromonomer does not include a monomer that provides a crosslinkable group.

A monomer that provides a crosslinking site is a monomer (cure site monomer) that provides a crosslinking site to the fluoropolymer for forming a crosslink with a curing agent. Monomers that provide a crosslinking site include monomers that provide a crosslinkable group.

In the present disclosure, the content of each monomer unit constituting the fluorine-containing elastomer can be calculated by appropriately combining NMR, FT-IR, elemental analysis, and X-ray fluorescence analysis depending on the type of monomer.

In this disclosure, "organic group" means a group containing one or more carbon atoms or a group formed by removing a hydrogen atom from an organic compound.
Examples of the "organic group" are:
an alkyl group which may have one or more substituents;
an alkenyl group optionally having one or more substituents;
an alkynyl group optionally having one or more substituents;
a cycloalkyl group optionally having one or more substituents,
a cycloalkenyl group optionally having one or more substituents,
a cycloalkadienyl group optionally having one or more substituents,
an aryl group which may have one or more substituents;
an aralkyl group which may have one or more substituents;
a non-aromatic heterocyclic group optionally having one or more substituents,
a heteroaryl group optionally having one or more substituents,
Cyano group,
Formyl group,
RaO-,
RaCO-,
_RaSO2- ,
RaCOO-,
RaNRaCO-,
RaCONRa-,
RaOCO-,
_RaOSO2- and
_RaNRbSO2-
(In these formulas, Ra is independently
an alkyl group which may have one or more substituents;
an alkenyl group optionally having one or more substituents;
an alkynyl group optionally having one or more substituents;
a cycloalkyl group optionally having one or more substituents,
a cycloalkenyl group optionally having one or more substituents,
a cycloalkadienyl group optionally having one or more substituents,
an aryl group which may have one or more substituents;
an aralkyl group which may have one or more substituents;
a non-aromatic heterocyclic group optionally having one or more substituents, or
a heteroaryl group optionally having one or more substituents,
Rb is independently H or an alkyl group which may have one or more substituents.
Includes:
The organic group is preferably an alkyl group which may have one or more substituents.

In addition, in this disclosure, a "substituent" means a group that can be substituted. Examples of the "substituent" include an aliphatic group, an aromatic group, a heterocyclic group, an acyl group, an acyloxy group, an acylamino group, an aliphatic oxy group, an aromatic oxy group, a heterocyclic oxy group, an aliphatic oxycarbonyl group, an aromatic oxycarbonyl group, a heterocyclic oxycarbonyl group, a carbamoyl group, an aliphatic sulfonyl group, an aromatic sulfonyl group, a heterocyclic sulfonyl group, an aliphatic sulfonyloxy group, an aromatic sulfonyloxy group, a heterocyclic sulfonyloxy group, a sulfamoyl group, an aliphatic sulfonamido group, an aromatic sulfonamido group, a heterocyclic sulfonamido group, an amino group, an aliphatic amino These include an aromatic amino group, an aromatic amino group, a heterocyclic amino group, an aliphatic oxycarbonylamino group, an aromatic oxycarbonylamino group, a heterocyclic oxycarbonylamino group, an aliphatic sulfinyl group, an aromatic sulfinyl group, an aliphatic thio group, an aromatic thio group, a hydroxy group, a cyano group, a sulfo group, a carboxy group, an aliphatic oxyamino group, an aromatic oxyamino group, a carbamoylamino group, a sulfamoylamino group, a halogen atom, a sulfamoylcarbamoyl group, a carbamoylsulfamoyl group, a dialiphatic oxyphosphinyl group, and a diaromatic oxyphosphinyl group.

The aliphatic group may be saturated or unsaturated, and may have a hydroxy group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the aliphatic group include alkyl groups having a total of 1 to 8 carbon atoms, preferably 1 to 4 carbon atoms, such as a methyl group, an ethyl group, a vinyl group, a cyclohexyl group, and a carbamoylmethyl group.

The aromatic group may have, for example, a nitro group, a halogen atom, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the aromatic group include aryl groups having 6 to 12 carbon atoms, preferably 6 to 10 carbon atoms in total, such as a phenyl group, a 4-nitrophenyl group, a 4-acetylaminophenyl group, and a 4-methanesulfonylphenyl group.

The heterocyclic group may have a halogen atom, a hydroxy group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the heterocyclic group include 5- to 6-membered heterocycles having a total of 2 to 12, preferably 2 to 10, carbon atoms, such as a 2-tetrahydrofuryl group and a 2-pyrimidyl group.

The acyl group may have an aliphatic carbonyl group, an arylcarbonyl group, a heterocyclic carbonyl group, a hydroxy group, a halogen atom, an aromatic group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the acyl group include acyl groups having a total of 2 to 8 carbon atoms, preferably 2 to 4 carbon atoms, such as an acetyl group, a propanoyl group, a benzoyl group, and a 3-pyridinecarbonyl group.

The acylamino group may have an aliphatic group, an aromatic group, a heterocyclic group, etc., such as an acetylamino group, a benzoylamino group, a 2-pyridinecarbonylamino group, a propanoylamino group, etc. Examples of the acylamino group include acylamino groups having a total of 2 to 12 carbon atoms, preferably 2 to 8 carbon atoms, and alkylcarbonylamino groups having a total of 2 to 8 carbon atoms, such as an acetylamino group, a benzoylamino group, a 2-pyridinecarbonylamino group, a propanoylamino group, etc.

The aliphatic oxycarbonyl group may be saturated or unsaturated, and may have a hydroxy group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the aliphatic oxycarbonyl group include alkoxycarbonyl groups having a total of 2 to 8 carbon atoms, preferably 2 to 4 carbon atoms, such as a methoxycarbonyl group, an ethoxycarbonyl group, and a (t)-butoxycarbonyl group.

The carbamoyl group may have an aliphatic group, an aromatic group, a heterocyclic group, etc. Examples of the carbamoyl group include an unsubstituted carbamoyl group, an alkylcarbamoyl group having a total of 2 to 9 carbon atoms, preferably an unsubstituted carbamoyl group, an alkylcarbamoyl group having a total of 2 to 5 carbon atoms, such as an N-methylcarbamoyl group, an N,N-dimethylcarbamoyl group, and an N-phenylcarbamoyl group.

The aliphatic sulfonyl group may be saturated or unsaturated, and may have a hydroxy group, an aromatic group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the aliphatic sulfonyl group include alkylsulfonyl groups having a total of 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms, such as a methanesulfonyl group.

The aromatic sulfonyl group may have a hydroxy group, an aliphatic group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the aromatic sulfonyl group include arylsulfonyl groups having a total of 6 to 10 carbon atoms, such as benzenesulfonyl groups.

The amino group may have an aliphatic group, an aromatic group, a heterocyclic group, etc.

The acylamino group may have, for example, an acetylamino group, a benzoylamino group, a 2-pyridinecarbonylamino group, a propanoylamino group, etc. Examples of the acylamino group include an acylamino group having a total of 2 to 12 carbon atoms, preferably a total of 2 to 8 carbon atoms, and more preferably an alkylcarbonylamino group having a total of 2 to 8 carbon atoms, such as an acetylamino group, a benzoylamino group, a 2-pyridinecarbonylamino group, a propanoylamino group, etc.

The above aliphatic sulfonamide group, aromatic sulfonamide group, and heterocyclic sulfonamide group may be, for example, a methanesulfonamide group, a benzenesulfonamide group, a 2-pyridine sulfonamide group, etc.

The sulfamoyl group may have an aliphatic group, an aromatic group, a heterocyclic group, etc. Examples of the sulfamoyl group include a sulfamoyl group, an alkylsulfamoyl group having a total of 1 to 9 carbon atoms, a dialkylsulfamoyl group having a total of 2 to 10 carbon atoms, an arylsulfamoyl group having a total of 7 to 13 carbon atoms, and a heterocyclic sulfamoyl group having a total of 2 to 12 carbon atoms, more preferably a sulfamoyl group, an alkylsulfamoyl group having a total of 1 to 7 carbon atoms, a dialkylsulfamoyl group having a total of 3 to 6 carbon atoms, an arylsulfamoyl group having a total of 6 to 11 carbon atoms, and a heterocyclic sulfamoyl group having a total of 2 to 10 carbon atoms, such as a sulfamoyl group, a methylsulfamoyl group, an N,N-dimethylsulfamoyl group, a phenylsulfamoyl group, and a 4-pyridine sulfamoyl group.

The aliphatic oxy group may be saturated or unsaturated and may have a methoxy group, an ethoxy group, an i-propyloxy group, a cyclohexyloxy group, a methoxyethoxy group, etc. Examples of the aliphatic oxy group include alkoxy groups having a total of 1 to 8 carbon atoms, preferably 1 to 6 carbon atoms, such as a methoxy group, an ethoxy group, an i-propyloxy group, a cyclohexyloxy group, a methoxyethoxy group, etc.

The aromatic amino group and heterocyclic amino group may have an aliphatic group, an aliphatic oxy group, a halogen atom, a carbamoyl group, a heterocyclic group condensed with the aryl group, an aliphatic oxycarbonyl group, preferably an aliphatic group having a total of 1 to 4 carbon atoms, an aliphatic oxy group having a total of 1 to 4 carbon atoms, a halogen atom, a carbamoyl group having a total of 1 to 4 carbon atoms, a nitro group, or an aliphatic oxycarbonyl group having a total of 2 to 4 carbon atoms.

The aliphatic thio group may be saturated or unsaturated and may be an alkylthio group having a total of 1 to 8 carbon atoms, more preferably 1 to 6 carbon atoms, such as a methylthio group, an ethylthio group, a carbamoylmethylthio group, or a t-butylthio group.

The carbamoylamino group may have an aliphatic group, an aryl group, a heterocyclic group, etc. Examples of the carbamoylamino group include a carbamoylamino group, an alkylcarbamoylamino group having a total of 2 to 9 carbon atoms, a dialkylcarbamoylamino group having a total of 3 to 10 carbon atoms, an arylcarbamoylamino group having a total of 7 to 13 carbon atoms, and a heterocyclic carbamoylamino group having a total of 3 to 12 carbon atoms, preferably a carbamoylamino group, an alkylcarbamoylamino group having a total of 2 to 7 carbon atoms, a dialkylcarbamoylamino group having a total of 3 to 6 carbon atoms, an arylcarbamoylamino group having a total of 7 to 11 carbon atoms, and a heterocyclic carbamoylamino group having a total of 3 to 10 carbon atoms, such as a carbamoylamino group, a methylcarbamoylamino group, an N,N-dimethylcarbamoylamino group, a phenylcarbamoylamino group, and a 4-pyridinecarbamoylamino group.

In this disclosure, ranges represented by endpoints include all numbers within that range (e.g., 1 to 10 includes 1.4, 1.9, 2.33, 5.75, 9.98, etc.).

In this disclosure, the term "at least 1" includes all numbers greater than or equal to 1 (e.g., at least 2, at least 4, at least 6, at least 8, at least 10, at least 25, at least 50, at least 100, etc.).

Specific embodiments of the present disclosure are described in detail below, but the present disclosure is not limited to the following embodiments.

In the manufacturing method disclosed herein, when an aqueous dispersion containing a fluorine-containing elastomer is produced by polymerizing a fluorine-containing monomer in the presence of an aqueous medium, after initiating the polymerization of the fluorine-containing monomer, a fluorine-containing compound (A) represented by general formula (A) is supplied to the polymerization system.

General formula (A): CX ⁱ X ^k = CX ^j R ^a -(CZ ¹ Z ² ) _k -Y ³ (A)
(In the formula, ^Xi , ^Xj and ^Xk are the same or different and are F, Cl, H or _CF3 ; ^Y3 is a hydrophilic group; ^Ra is a linking group; ^Z1 and ^Z2 are the same or different and are H, F or _CF3 ; and k is 0 or 1. However, at least one of Xi, ^Xk , ^Xj , ^Ra , ^{Z1 and Z2} contains F. The number of carbon atoms in the portion excluding the hydrophilic group is 6 or less.)

By supplying the fluorine-containing compound (A) to the polymerization system after the start of polymerization, even if the amount of fluorine-containing compound (A) supplied is relatively small, adhesion of the fluorine-containing elastomer produced by the polymerization reaction to the polymerization tank can be suppressed, and the polymerization reaction of the fluorine-containing monomer can proceed smoothly, producing a sufficient number of fluorine-containing elastomer particles.

The fluorine-containing compound (A) used in the production method of the present disclosure is characterized in that the carbon number excluding the hydrophilic group (Y ³ ) is 6 or less and the portion corresponding to the hydrophobic group in the molecule has a short chain structure. If the carbon number excluding the hydrophilic group (Y ³ ) exceeds 6, it becomes necessary to use a relatively large amount of the compound in order to suppress adhesion of the fluorine-containing elastomer to the polymerization tank, which is economically disadvantageous and also disadvantageous in that post-treatment becomes complicated.

The number of carbon atoms in the portion of the fluorine-containing compound (A) excluding the hydrophilic group (Y ³ ) is preferably 3 or more, more preferably 4 or more, and even more preferably 5 or more, since this allows the polymerization of the fluorine-containing monomer to proceed more smoothly while further suppressing the adhesion of the fluorine-containing elastomer to the polymerization tank.

The hydrophilic group (Y ³ ) of the fluorine-containing compound (A) may be any group exhibiting hydrophilicity, and may be an anionic hydrophilic group, a cationic hydrophilic group or a nonionic hydrophilic group, but is preferably an anionic hydrophilic group.

Examples of the hydrophilic group (Y ³ ) in the fluorine-containing compound (A) include -NH ₂ , -P(O)(OM) ₂ , -OP(O)(OM) ₂ , -SO ₃ M, -OSO ₃ M, and -COOM (in each formula, M is H, a metal atom, NR ⁷ ₄ , an imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent, and R ⁷ is H or an organic group, which may be the same or different. Any two of them may be bonded to each other to form a ring). Of these, the hydrophilic group is preferably -SO ₃ M or -COOM, and more preferably -COOM. The organic group for R ⁷ is preferably an alkyl group. As R ⁷ , H or a C _1-10 organic group is preferable, H or a C _1-4 organic group is more preferable, H or a C _1-4 alkyl group is even more preferable, and H is most preferable. The metal atom may be a monovalent or divalent metal atom, preferably an alkali metal (group 1) or an alkaline earth metal (group 2), more preferably Na, K or Li.

In the general formula (A), R ^a is a linking group. In the present disclosure, the term "linking group" refers to a divalent linking group. As the linking group, a single bond or a group containing at least one carbon atom is preferred. The number of carbon atoms in the linking group is selected so that the number of carbon atoms in the portion excluding the hydrophilic group of the fluorine-containing compound (A) is 6 or less.

The linking group may be linear or branched, cyclic or acyclic, saturated or unsaturated, substituted or unsubstituted, and may optionally contain one or more heteroatoms selected from the group consisting of sulfur, oxygen, and nitrogen, and may optionally contain one or more functional groups selected from the group consisting of esters, amides, sulfonamides, carbonyls, carbonates, urethanes, ureas, and carbamates. The linking group may not contain carbon atoms, but may be a catenary heteroatom such as oxygen, sulfur, or nitrogen.

R ^a is preferably, for example, a catenary heteroatom such as oxygen, sulfur or nitrogen, or a divalent organic group.

When R ^a is a divalent organic group, the hydrogen atom bonded to the carbon atom may be replaced with a halogen other than fluorine, such as chlorine, and may or may not contain a double bond. R ^a may be either linear or branched, and may be either cyclic or non-cyclic. R ^a may also contain a functional group (e.g., ester, ether, ketone, amine, halide, etc.).

R ^a may also be a non-fluorinated divalent organic group, or a partially fluorinated or perfluorinated divalent organic group.

R ^a may be, for example, a hydrocarbon group in which no fluorine atom is bonded to a carbon atom, a hydrocarbon group in which some of the hydrogen atoms bonded to the carbon atom are substituted with fluorine atoms, a hydrocarbon group in which all of the hydrogen atoms bonded to the carbon atom are substituted with fluorine atoms, -(C=O)-, -(C=O)-O-, or a hydrocarbon group containing an ether bond, which may contain an oxygen atom, a double bond, or a functional group.

R ^a is preferably -(C=O)-, -(C=O)-O-, or a hydrocarbon group having 1 to 4 carbon atoms which may contain an ether bond and which may contain a carbonyl group, and in the hydrocarbon group, some or all of the hydrogen atoms bonded to the carbon atoms may be substituted with fluorine.

R ^a is preferably a fluorinated alkylene group or a fluorinated oxyalkylene group. These are preferably linear. The number of carbon atoms is selected so that the carbon number of the moiety excluding the hydrophilic group of the fluorine-containing compound (A) is 6 or less.

As the fluorine-containing compound (A), a fluorine-containing compound represented by the general formula (A1): can be used since it can further suppress the adhesion of the fluorine-containing elastomer to the polymerization vessel while more smoothly promoting the polymerization of the fluorine-containing monomer:
CX ⁱ X ^k =CX ^j -OR-(CZ ¹ Z ² ) _k -Y ³
(wherein Xi, ^Xj , ^Xk , ^Z1 , ^Z2 , k ^{and Y3} are as defined above, and R is a fluorinated alkylene group or a fluorinated oxyalkylene group having 1 to 3 carbon atoms), and a compound represented by general formula (A2):
CX ⁱ X ^k =CX ^j -CZ ¹ Z ² -O-R-(CZ ¹ Z ² ) _k -Y ³
(wherein Xi, ^Xj , ^Xk , ^Z1 , ^Z2 , k ^{and Y3} are as defined above, and R is a fluorinated alkylene group or a fluorinated oxyalkylene group having 1 or 2 carbon atoms) is preferred.

As the fluorine-containing compound (A), among others,
CF ₂ =CFOCF ₂ −Y ³ ,
CF ₂ =CFOCF ₂ CF ₂ -Y ³ ,
CF ₂ =CFOCF ₂ CF ₂ CF ₂ -Y ³ ,
CF ₂ =CFOCF ₂ CF ₂ CH ₂ -Y ³ ,
CF ₂ =CFOCF ₂ CF ₂ CF ₂ CF ₂ -Y ³ ,
CF ₂ =CFOCF ₂ CF(CF ₃ )OCF ₂ -Y ³ ,
CF ₂ =CFOCF ₂ CF ₂ OCF(CF ₃ )-Y ³ ,
CF ₂ =CFOCF ₂ CF ₂ OCF ₂ -Y ³ ,
_CH2 = _CFCF2OCF2 - _Y3 ^,
_CH2 = _CFCF2OCF ( _CF3 ) ^-Y3 ,
_CH2 = _{CFCF2OCH2CF2 - Y3} ^,
_CH2 = _{CFCF2OCF2CF2 - Y3} ^,
_CH2 = _{CFCF2OCF2CH2 - Y3} ^,
_{CH2 = CFCF2OCH2CF2CH2 - Y3} ^,
_{CH2 = CFCF2OCF2CF2CH2 - Y3} ^,
_{CH2 = CFCF2OCF2CF2CF2 - Y3} ^,
_CH2 = _CFCF2OCF ( _CF3 ) _CH2 - ^Y3 ,
_CH2 = _CFCF2OCF ( _CF3 ) _CF2 - ^Y3 ,
_CH2 ⁼ _{CFCF2OCF2CF2OCF2 - Y3 ,}
CF ₂ =CFCF ₂ OCF ₂ CF ₂ CF ₂ -Y ³ ,
CF ₂ =CFCF ₂ OCF ₂ CF(CF ₃ )-Y ³ ,
CF ₂ =CFCF ₂ OCF(CF ₃ )-Y ³ ,
_CF2 = _CFCF2OCF ( _CF3 ) _CH2 - ^Y3 ,
CF ₂ =CFCF ₂ OCF(CF ₃ )CF ₂ -Y ³ ,
is preferred.

The method of supplying the fluorine-containing compound (A) is not particularly limited, and the entire amount may be supplied all at once at one time after the start of polymerization, or the fluorine-containing compound may be supplied continuously or intermittently after the start of polymerization. For example, when the fluorine-containing monomer is supplied continuously or intermittently to the polymerization system, the fluorine-containing compound (A) may be supplied intermittently from the time when the supply amount of the fluorine-containing monomer reaches a given amount until the supply amount of the fluorine-containing monomer reaches a given time.

The timing of supplying the fluorine-containing compound (A) is not particularly limited as long as it is after the start of polymerization. In the case where the fluorine-containing monomer is continuously or intermittently supplied to the polymerization system, the preferred supply time point when the fluorine-containing compound (A) is supplied all at once, or the preferred supply time when the fluorine-containing compound (A) is supplied continuously or intermittently, are exemplified below.

When the fluorine-containing compound (A) is supplied all at once at one time point after the start of polymerization, it is preferable to supply the fluorine-containing compound (A) after the amount (g) of the fluorine-containing monomer supplied after the start of polymerization reaches 5% of the total amount (g) of the fluorine-containing monomer supplied after the start of polymerization. It is also preferable to supply the fluorine-containing compound (A) after the amount of the fluorine-containing monomer supplied after the start of polymerization reaches 10%, 20%, 30% or 40%.

In addition, when the fluorine-containing compound (A) is supplied all at once at one time point after the start of polymerization, it is preferable to supply the fluorine-containing compound (A) before the amount (g) of the fluorine-containing monomer supplied after the start of polymerization reaches 90% of the total amount (g) of the fluorine-containing monomer supplied after the start of polymerization. In addition, it is preferable to supply the fluorine-containing compound (A) before the amount of the fluorine-containing monomer supplied after the start of polymerization reaches 85%, 80%, 75% or 70%.

When the fluorine-containing compound (A) is supplied continuously or intermittently, adhesion of the fluorine-containing elastomer to the polymerization tank can be further suppressed, so it is preferable to start supplying the fluorine-containing compound (A) after the amount (g) of the fluorine-containing monomer supplied after the start of polymerization reaches 5% of the total amount (g) of the fluorine-containing monomer supplied after the start of polymerization. It is also preferable to start supplying the fluorine-containing compound (A) after the amount of the fluorine-containing monomer supplied after the start of polymerization reaches 10%, 20%, 30% or 40%.

In addition, when the fluorine-containing compound (A) is supplied continuously or intermittently, it is preferable to stop the supply of the fluorine-containing compound (A) before the amount (g) of the fluorine-containing monomer supplied after the start of polymerization reaches 90% of the total amount (g) of the fluorine-containing monomer supplied after the start of polymerization, since this can further suppress adhesion of the fluorine-containing elastomer to the polymerization tank. In addition, it is preferable to stop the supply of the fluorine-containing compound (A) before the amount of the fluorine-containing monomer supplied after the start of polymerization reaches 85%, 80%, 75% or 70%.

The fluorine-containing compound (A) may be supplied immediately after the start of polymerization, and after the polymerization reaction has proceeded for a certain period of time, the fluorine-containing compound (A) may be further supplied. For example, when the fluorine-containing monomer is continuously or intermittently supplied to the polymerization system, the fluorine-containing compound (A) may be supplied immediately after the start of polymerization, and the fluorine-containing compound (A) may be further supplied after a certain amount of the fluorine-containing monomer has been supplied. This supply method not only suppresses adhesion of the fluorine-containing elastomer to the polymerization tank, but also increases the number of particles of the fluorine-containing elastomer generated by polymerization, and allows the polymerization of the fluorine-containing monomer to proceed more smoothly. In the present disclosure, "immediately after the start of polymerization" refers to, for example, the period before the amount of the fluorine-containing monomer supplied after the start of polymerization (g) reaches 1% of the total amount of the fluorine-containing monomer supplied after the start of polymerization, when the fluorine-containing monomer is continuously or intermittently supplied to the polymerization system. When the fluorine-containing compound (A) is further supplied after the polymerization reaction has proceeded for a certain period of time (after a certain amount of the fluorine-containing monomer has been supplied), the supply time or timing of the fluorine-containing compound (A) can be the preferred supply time when the fluorine-containing compound (A) is supplied all at once, or the preferred supply timing when the fluorine-containing compound (A) is supplied continuously or intermittently, as exemplified above.

Since the polymerization of a fluorine-containing monomer is usually initiated by the addition of a polymerization initiator to the polymerization system, the time when the polymerization reaction of the fluorine-containing monomer is initiated is usually the time when the polymerization initiator is added to the polymerization system, and when the polymerization initiator is added to the polymerization system continuously or intermittently, it is the time when the polymerization initiator is first added to the polymerization system. In this disclosure, "after the start of polymerization" refers to the polymerization period from the time when the polymerization initiator is first added to the polymerization system to the time when the polymerization reaction of the fluorine-containing monomer is completed. In this disclosure, "before the start of polymerization" refers to the time when the polymerization initiator is first added to the polymerization system and the period before that time.

The amount of fluorine-containing compound (A) supplied after the initiation of polymerization of the fluorine-containing monomer is preferably 30 to 5000 ppm by mass relative to the aqueous medium, more preferably 80 ppm by mass or more, even more preferably 130 ppm by mass or more, particularly preferably 150 ppm by mass or more, most preferably 180 ppm by mass or more, and more preferably 1000 ppm by mass or less, even more preferably 500 ppm by mass or less, particularly preferably 450 ppm by mass or less. By setting the amount of fluorine-containing compound (A) supplied after the initiation of polymerization of the fluorine-containing monomer within the above range, the polymerization of the fluorine-containing monomer can be more smoothly promoted while further suppressing adhesion of the fluorine-containing elastomer to the polymerization tank.

Furthermore, in the production method of the present disclosure, the amount of fluorine-containing compound (A) supplied after the initiation of polymerization of the fluorine-containing monomer may be 300 ppm by mass or less, 250 ppm by mass or less, or 200 ppm by mass or less. Since the production method of the present disclosure uses a fluorine-containing compound (A) having a specific structure, even when the amount of fluorine-containing compound (A) supplied is extremely small, the polymerization of the fluorine-containing monomer can be smoothly carried out while suppressing adhesion of the fluorine-containing elastomer to the polymerization tank.

In the present disclosure, the amount of fluorine-containing compound (A) supplied after the initiation of polymerization refers to the amount of fluorine-containing compound (A) supplied to the polymerization system after the initiation of polymerization of the fluorine-containing monomer until the completion of the polymerization reaction of the fluorine-containing monomer, and does not include the amount of fluorine-containing compound (A) supplied to the polymerization system at or before the start of the polymerization reaction of the fluorine-containing monomer.

In the production method of the present disclosure, the fluorine-containing compound (A) is supplied after the initiation of polymerization of the fluorine-containing monomer, but it is preferable to also supply the fluorine-containing compound (A) before the initiation of polymerization of the fluorine-containing monomer. By supplying the fluorine-containing compound (A) before the initiation of polymerization of the fluorine-containing monomer, the number of fluorine-containing elastomer particles generated by polymerization can be increased, and the polymerization of the fluorine-containing monomer can be made to proceed more smoothly.

The amount of fluorine-containing compound (A) supplied before the start of polymerization of the fluorine-containing monomer is preferably 5 to 5000 ppm by mass, more preferably 10 ppm by mass or more, even more preferably 15 ppm by mass or more, more preferably 1000 ppm by mass or less, even more preferably 500 ppm by mass or less, particularly preferably 300 ppm by mass or less, and most preferably 200 ppm by mass or less, relative to the aqueous medium. By setting the amount of fluorine-containing compound (A) supplied before the start of polymerization of the fluorine-containing monomer within the above range, many fluorine-containing elastomer particles can be generated, and the polymerization of the fluorine-containing monomer can proceed more smoothly.

Furthermore, in the production method of the present disclosure, the amount of fluorine-containing compound (A) supplied before the start of polymerization of the fluorine-containing monomer may be 150 ppm by mass or less, 100 ppm by mass or less, or 70 ppm by mass or less. Since the production method of the present disclosure uses a fluorine-containing compound (A) having a specific structure, even if the amount of fluorine-containing compound (A) supplied before the start of polymerization is extremely small, a sufficient number of fluorine-containing elastomer particles can be generated, and the polymerization of the fluorine-containing monomer can be smoothly promoted.

When the fluorine-containing compound (A) is supplied before or after the start of polymerization, the total amount of the fluorine-containing compound (A) supplied before the start of polymerization of the fluorine-containing monomer and the total amount of the fluorine-containing compound (A) supplied after the start of polymerization of the fluorine-containing monomer is preferably 30 to 5000 ppm by mass, more preferably 100 ppm by mass or more, even more preferably 150 ppm by mass or more, particularly preferably 200 ppm by mass or more, most preferably 250 ppm by mass or more, and more preferably 1000 ppm by mass or less, and even more preferably 500 ppm by mass or less, relative to the aqueous medium. By setting the total amount of the fluorine-containing compound (A) supplied within the above range, it is possible to generate more fluorine-containing elastomer particles at a higher polymerization rate while further suppressing adhesion of the fluorine-containing elastomer to the polymerization tank, and furthermore, it is possible to proceed with the polymerization of the fluorine-containing monomer more smoothly.

Furthermore, in the production method of the present disclosure, when the fluorine-containing compound (A) is supplied before and after the start of polymerization, the total amount of the fluorine-containing compound (A) supplied before the start of polymerization of the fluorine-containing monomer and the amount of the fluorine-containing compound (A) supplied after the start of polymerization of the fluorine-containing monomer may be 450 ppm by mass or less, 400 ppm by mass or less, 350 ppm by mass or less, 300 ppm by mass or less, or 250 ppm by mass or less. Since the production method of the present disclosure uses a fluorine-containing compound (A) having a specific structure, even if the total amount of the fluorine-containing compound (A) supplied is extremely small, a sufficient number of fluorine-containing elastomer particles can be generated at a sufficient polymerization rate while suppressing adhesion of the fluorine-containing elastomer to the polymerization tank, and further, the polymerization of the fluorine-containing monomer can be smoothly promoted.

When the fluorine-containing compound (A) is supplied before or after the start of polymerization, the mass ratio ((a)/(b)) of the amount (a) of the fluorine-containing compound (A) supplied before the start of polymerization to the amount (b) of the fluorine-containing compound (A) supplied after the start of polymerization is preferably 1/20 to 2/1, more preferably 1/10 to 1/1, and even more preferably 1/10 to 7/10. By setting the mass ratio ((a)/(b)) within the above range, it is possible to generate more fluorine-containing elastomer particles at a higher polymerization rate while further suppressing adhesion of the fluorine-containing elastomer to the polymerization tank, and furthermore, it is possible to proceed with the polymerization of the fluorine-containing monomer more smoothly.

As a method for supplying the fluorine-containing compound (A), for example, a method of supplying the fluorine-containing compound (A) from a pipe connected to the polymerization tank using a pump can be mentioned. The supply rate of the fluorine-containing compound (A) may be constant or may be changed. The fluorine-containing compound (A) may also be continuously added dropwise. Alternatively, the fluorine-containing compound (A) may be dissolved or dispersed in water to prepare an aqueous solution of the fluorine-containing compound (A), and then the aqueous solution of the fluorine-containing compound (A) may be supplied.

In the manufacturing method of the present disclosure, the polymerization of the fluorine-containing monomer can be carried out, for example, by charging an aqueous medium into a pressure-resistant polymerization tank equipped with a stirrer, deoxidizing, charging the monomer, bringing the temperature to a predetermined level, adding a polymerization initiator to start polymerization, and supplying the fluorine-containing compound (A) to the polymerization tank after the start of polymerization. In addition to supplying the fluorine-containing compound (A) to the polymerization tank after the start of polymerization, the fluorine-containing compound (A) may also be supplied to the polymerization tank before the start of polymerization. Since the pressure decreases as the reaction progresses, additional monomer is continuously or intermittently supplied to maintain the initial pressure, and when a predetermined amount of monomer has been supplied, the supply is stopped, the monomer in the reaction vessel is purged, and the temperature is returned to room temperature to terminate the reaction.

In the manufacturing method of the present disclosure, polymerization may be carried out in the presence of a polymerization initiator.

The polymerization initiator may be a radical polymerization initiator. The polymerization initiator is not particularly limited as long as it can generate radicals at the temperature at which the fluorine-containing monomer is polymerized. Oil-soluble polymerization initiators, water-soluble polymerization initiators, etc. may be used, but water-soluble polymerization initiators are preferred. The polymerization initiator may also be used as a redox initiator in combination with a reducing agent, etc.

The amount of polymerization initiator used when polymerizing a fluorine-containing monomer is determined appropriately depending on the type of monomer, the molecular weight of the desired fluorine-containing elastomer, and the reaction rate. The amount of polymerization initiator is determined appropriately depending on the molecular weight of the desired fluorine-containing elastomer and the polymerization reaction rate, but is preferably 0.00001 to 10% by mass, and more preferably 0.0001 to 1% by mass, relative to 100% by mass of the total amount of monomer.

As a polymerization initiator, an oil-soluble radical polymerization initiator, a water-soluble radical polymerization initiator, or an azo compound can be used.

The oil-soluble radical polymerization initiator may be a known oil-soluble peroxide, for example, dialkyl peroxycarbonates such as diisopropyl peroxydicarbonate and disec-butyl peroxydicarbonate, peroxyesters such as t-butyl peroxyisobutyrate and t-butyl peroxypivalate, dialkyl peroxides such as di-t-butyl peroxide, and also di(ω-hydro-dodecafluoroheptanoyl) peroxide, di(ω-hydro-tetradecafluorooctanoyl) peroxide, di(ω-hydro-hexadecafluorononanoyl) peroxide, di(perfluorobutyryl) peroxide, di(perfluorovaleryl) peroxide, di(perfluorohexanoyl) peroxide, di(perfluoroheptanoyl) peroxide, di(perfluorooctanoyl) peroxide, di(perfluorononanoyl) peroxide, di(ω-chloro Representative examples of the perfluoro(or fluorochloro)acyl]peroxides include di(ω-hexafluorobutyryl)peroxide, di(ω-chloro-decafluorohexanoyl)peroxide, di(ω-chloro-tetradecafluorooctanoyl)peroxide, ω-hydro-dodecafluoroheptanoyl-ω-hydrohexadecafluorononanoyl-peroxide, ω-chloro-hexafluorobutyryl-ω-chloro-decafluorohexanoyl-peroxide, ω-hydrododecafluoroheptanoyl-perfluorobutyryl-peroxide, di(dichloropentafluorobutanoyl)peroxide, di(trichlorooctafluorohexanoyl)peroxide, di(tetrachloroundecafluorooctanoyl)peroxide, di(pentachlorotetradecafluorodecanoyl)peroxide, and di(undecachlorodotriacontafluorodocosanoyl)peroxide.

Examples of azo compounds include azodicarboxylate, azodicarboxylamide, 2,2'-azobisisobutyronitrile, 2,2'-azobis 2,4-dimethylvaleronitrile, 2,2'-azobis(2-methylpropionamidine) dihydrochloride, and 4,4'-azobis(4-cyanovaleric acid).

The water-soluble radical polymerization initiator may be a known water-soluble peroxide, such as ammonium, potassium, or sodium salts of persulfuric acid, perboric acid, perchloric acid, perphosphoric acid, or percarbonic acid; organic peroxides such as disuccinic acid peroxide or diglutaric acid peroxide; t-butyl permaleate; or t-butyl hydroperoxide. A reducing agent such as sulfites may also be included, and the amount used may be 0.1 to 20 times the amount of the peroxide.

As the water-soluble peroxide, a salt of persulfuric acid is preferable because the amount of radicals generated can be easily adjusted. Potassium persulfate (K ₂ S ₂ O ₈ ), ammonium persulfate ((NH ₄ ) ₂ S ₂ O ₈ ), and sodium persulfate (Na ₂ S ₂ O ₈ ) are preferable, and ammonium persulfate is most preferable.

When polymerization is carried out using water-soluble peroxides at a polymerization temperature of 45°C or higher, it is preferable to polymerize without using a reducing agent.

For example, when polymerization is carried out at a low temperature of 60°C or less, it is preferable to use a redox initiator that combines an oxidizing agent and a reducing agent as the polymerization initiator. In other words, it is preferable to carry out the above polymerization in the presence of a redox initiator.

Examples of oxidizing agents include persulfates, organic peroxides, potassium permanganate, manganese triacetate, cerium ammonium nitrate, and bromates. Examples of reducing agents include sulfites, bisulfites, bromates, diimines, oxalic acid, and metal sulfinates. Examples of persulfates include ammonium persulfate, potassium persulfate, and sodium persulfate. Examples of sulfites include sodium sulfite and ammonium sulfite. In order to increase the decomposition rate of the initiator, it is also preferable to add a copper salt or an iron salt to the combination of redox initiators. Examples of copper salts include copper(II) sulfate, and examples of iron salts include iron(II) sulfate. In addition, when using copper salts or iron salts, it is particularly preferable to add a chelating agent. As a chelating agent, disodium salt of ethylenediaminetetraacetic acid dihydrate is preferable.

Examples of redox initiators include potassium permanganate/oxalic acid, ammonium persulfate/bisulfite/ferrous sulfate, ammonium persulfate/sulfite/ferrous sulfate, ammonium persulfate/sulfite, ammonium persulfate/ferrous sulfate, manganese triacetate/oxalic acid, cerium ammonium nitrate/oxalic acid, bromate/sulfite, bromate/bisulfite, ammonium persulfate/sodium hydroxymethanesulfinate dihydrate, and the like, with ammonium persulfate/sodium hydroxymethanesulfinate dihydrate being preferred.

When a redox initiator is used, either the oxidizing agent or the reducing agent may be charged in advance to the polymerization tank, and then the other may be added continuously or intermittently to initiate polymerization. For example, when ammonium persulfate/sodium hydroxymethanesulfinate dihydrate is used, it is preferable to charge ammonium persulfate in the polymerization tank and continuously add sodium hydroxymethanesulfinate dihydrate thereto.

The amount of persulfate used in the redox initiator is preferably 0.001 to 2.0 mass %, more preferably 0.01 to 1.5 mass %, and particularly preferably 0.05 to 1.0 mass %, relative to the above-mentioned aqueous medium used for polymerization.

The amount of reducing agent used is preferably 1 to 30% by mass, more preferably 3 to 25% by mass, and particularly preferably 5 to 20% by mass, relative to the aqueous medium used for polymerization.

In addition, the amount of the third component (the above copper salt, iron salt, etc.) used is preferably 0.001 to 0.5 mass %, more preferably 0.005 to 0.4 mass %, and particularly preferably 0.01 to 0.3 mass %, relative to the above aqueous medium used in the polymerization.

In the production method of the present disclosure, the fluorine-containing monomer may be polymerized in the presence of a chain transfer agent. As the chain transfer agent, a known one may be used, for example, a hydrocarbon, an ester, an ether, an alcohol, a ketone, a halogen-containing compound, a carbonate, etc. Among them, isopentane, diethyl malonate, and ethyl acetate are preferred from the viewpoint of being unlikely to decrease the reaction rate, and diiodine compounds such as I(CF ₂ ) ₄ I, I(CF ₂ ) ₆ I, and ICH ₂ I are preferred from the viewpoint of being capable of iodinating the polymer terminal and being usable as a reactive polymer.

As the chain transfer agent, it is particularly preferable to use a bromine compound or an iodine compound. Examples of polymerization methods using a bromine compound or an iodine compound include iodine transfer polymerization and bromine transfer polymerization.

Iodine compounds and bromine compounds are water-insoluble and difficult to emulsify. Therefore, emulsion polymerization is inherently limited, and there has been a tendency to require the use of large amounts of surfactants. The manufacturing method disclosed herein makes it possible to obtain a fluorine-containing elastomer by polymerization using an iodine compound or a bromine compound, for example, iodine transfer polymerization or bromine transfer polymerization, even in the absence of surfactants that have been used conventionally.

Iodine transfer polymerization is a method that utilizes living radical polymerization by a radical chain reactivation mechanism, which occurs due to the low dissociation energy of the carbon-iodine bond, which is radically active and involves a chain transfer reaction during the radical polymerization reaction. The reaction conditions can be appropriately selected from known conditions and are not particularly limited. For example, the conditions described in "Collection of Polymers, Vol. 49, No. 10, pp. 765-783, October 1992" and JP-A-53-3495 can be appropriately adopted. A similar polymerization can be performed using a bromine compound instead of an iodine compound, and in this disclosure, such polymerization is referred to as bromine transfer polymerization.

Among these, iodine transfer polymerization is preferred in terms of polymerization reactivity, crosslinking reactivity, etc.

Representative examples of the bromine compound or iodine compound include compounds represented by the general formula:
^R8IxBr _{y ​}
(wherein x and y are each an integer of 0 to 2 and satisfy 1≦x+y≦2, and ^R8 is a saturated or unsaturated fluorohydrocarbon group or chlorofluorohydrocarbon group having 1 to 16 carbon atoms, or a hydrocarbon group having 1 to 3 carbon atoms, which may contain an oxygen atom). By using a bromine compound or iodine compound, iodine or bromine is introduced into the polymer and functions as a crosslinking point.

Examples of the bromine compounds and iodine compounds include 1,3-diiodoperfluoropropane, 2-iodoperfluoropropane, 1,3-diiodo-2-chloroperfluoropropane, 1,4-diiodoperfluorobutane, 1,5-diiodo-2,4-dichloroperfluoropentane, 1,6-diiodoperfluorohexane, 1,8-diiodoperfluorooctane, 1,12-diiodoperfluorododecane, 1,16-diiodoperfluorohexadecane, diiodomethane, 1,2-diiodoethane, 1,3-diiodo-n-propane, CF ₂ Br ₂ , BrCF 2 CF ₂ Br, CF ₃ CFBrCF ₂ Br, CFClBr ₂ , _{BrCF 2 CFClBr} , CFBrClCFClBr, BrCF ₂ Examples of such compounds include CF ₂ CF ₂ Br, BrCF ₂ CFBrOCF ₃ , 1-bromo-2-iodoperfluoroethane, 1-bromo-3-iodoperfluoropropane, 1-bromo-4-iodoperfluorobutane, 2-bromo-3-iodoperfluorobutane, 3-bromo-4-iodoperfluorobutene-1, 2-bromo-4-iodoperfluorobutene-1, monoiodomonobromo-substituted benzene, diiodomonobromo-substituted benzene, and (2-iodoethyl) and (2-bromoethyl)-substituted benzene. These compounds may be used alone or in combination with each other.
Among these, from the viewpoints of polymerization reactivity, crosslinking reactivity, availability, and the like, compounds that do not contain bromine and contain only iodine are preferred, and it is preferable to use 1,4-diiodoperfluorobutane, 1,6-diiodoperfluorohexane, or 2-iodoperfluoropropane.

The amount of the chain transfer agent is preferably 0.2×10 ⁻³ to 2 mol %, more preferably 1.0×10 ⁻³ to 1 mol %, based on the total amount of monomers used in the polymerization.

The aqueous medium means a liquid containing water. The aqueous medium is not particularly limited as long as it contains water, and may contain water and, for example, a fluorine-free organic solvent such as an alcohol, ether, or ketone, and/or a fluorine-containing organic solvent having a boiling point of 40° C. or less.

In the polymerization of fluorine-containing monomers, phosphates, sodium hydroxide, potassium hydroxide, ammonia water, etc. may be used as pH adjusters.

The aqueous medium is preferably acidic. By polymerizing the fluorine-containing monomer in the presence of the fluorine-containing compound (A) using an acidic aqueous medium, adhesion of the fluorine-containing polymer to the polymerization tank can be further suppressed. The pH of the aqueous medium is preferably 7 or less, more preferably 6 or less, and preferably 3 or more.

In the manufacturing method disclosed herein, the fluorine-containing monomer may be polymerized in the presence or absence of fluorine-containing monomer polymerization seed particles.

The above-mentioned "fluorine-containing monomer polymerization seed particles" are obtained by polymerizing a fluorine-containing monomer in an aqueous medium, and are present during the second polymerization in which the types and proportions of components such as monomers and additives (e.g., polymerization initiators) that constitute the polymerization reaction system, and reaction conditions, etc. are different. The fluorine-containing monomer polymerization seed particles act as so-called seed particles during the polymerization of the fluorine-containing monomer, and constitute the polymerization of the fluorine-containing monomer in the presence of the seed particles, that is, the so-called seed polymerization. In the production method disclosed herein, such seed polymerization may not be performed when polymerizing the fluorine-containing monomer.

In the manufacturing method of the present disclosure, the polymerization temperature for polymerizing the fluorine-containing monomer is preferably 10 to 120°C, more preferably 20 to 100°C. From the viewpoints of the stability of the aqueous dispersion and the reduction of the adhesion rate, the polymerization temperature is preferably 15 to 60°C, more preferably 18 to 55°C, and even more preferably 20 to 50°C. The polymerization temperature is preferably 60 to 120°C, more preferably 60 to 100°C, and even more preferably 70 to 90°C, since a fluorine-containing elastomer that has a high polymerization rate and gives a molded product with excellent physical properties can be obtained.

In the manufacturing method disclosed herein, the polymerization pressure for polymerizing the fluorine-containing monomer is preferably 0.5 to 10 MPaG, and more preferably 1 to 7 MPaG.

In the manufacturing method of the present disclosure, a fluorine-containing monomer is polymerized in the presence of a fluorine-containing compound (A) and an aqueous medium, and therefore adhesion of the polymer (fluorine-containing elastomer) to the polymerization tank can be suppressed. The rate of polymer adhesion to the polymerization tank is preferably 8% by mass or less, more preferably 4% by mass or less, even more preferably 3% by mass or less, and most preferably 2% by mass or less.

The polymer adhesion rate is the ratio of the mass of the polymer adhesion that adheres to the polymerization tank after the polymerization is completed to the total amount of the polymer (fluoroelastomer) after the polymerization is completed (the adhesion rate to the polymerization tank). The polymer adhesion includes the polymer that adheres to the inside of the polymerization tank, such as the inner wall of the polymerization tank and the stirring blades, after the aqueous dispersion is extracted from the polymerization tank after the polymerization is completed, and the polymer that is liberated from the aqueous dispersion by aggregation and floats or precipitates without being dispersed in the aqueous dispersion. The mass of the polymer adhesion is the mass after the moisture contained in the polymer adhesion is removed by drying at 120°C.
Polymer adhesion rate (mass %)=mass of polymer adhesion/mass of obtained polymer (including adhesion)×100
Mass of obtained polymer=mass of aqueous dispersion×solids concentration of aqueous dispersion (mass%)/100+mass of polymer deposit

In the manufacturing method of the present disclosure, an aqueous dispersion of a fluorine-containing elastomer is obtained by polymerizing a fluorine-containing monomer. The fluorine-containing monomer is preferably a fluorine-containing monomer (excluding the fluorine-containing compound (A)), and more preferably does not contain a hydrophilic group.

Examples of the fluorine-containing monomer include vinylidene fluoride (VdF), tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoro(alkyl vinyl ether) (PAVE), chlorotrifluoroethylene (CTFE), trifluoroethylene, trifluoropropylene, tetrafluoropropylene, pentafluoropropylene, trifluorobutene, tetrafluoroisobutene, hexafluoroisobutene, vinyl fluoride, iodine-containing fluorinated vinyl ether, and compounds represented by the general formula (2):
CHX ¹ =CX ² Rf (2)
(wherein one of ^X1 and ^X2 is H and the other is F, and Rf is a linear or branched fluoroalkyl group having 1 to 12 carbon atoms)

As PAVE, perfluoro(methyl vinyl ether) (PMVE), perfluoro(ethyl vinyl ether) (PEVE), and perfluoro(propyl vinyl ether) (PPVE) are more preferred, with PMVE being particularly preferred.

Also usable as the PAVE is a perfluorovinyl ether represented by the formula: CF ₂ ═CFOCF ₂ ORf ^c (wherein Rf ^c is a linear or branched perfluoroalkyl group having 1 to 6 carbon atoms, a cyclic perfluoroalkyl group having 5 to 6 carbon atoms, or a linear or branched perfluorooxyalkyl group having 2 to 6 carbon atoms and containing 1 to 3 oxygen atoms). As the PAVE, for example, CF ₂ ═CFOCF ₂ OCF ₃ , CF ₂ ═CFOCF ₂ OCF ₂ CF ₃ , or CF ₂ ═CFOCF ₂ OCF ₂ CF ₂ OCF ₃ are preferred.

As the fluorine-containing monomer (2), a monomer in which Rf is a linear fluoroalkyl group is preferred, and a monomer in which Rf is a linear perfluoroalkyl group is more preferred. The number of carbon atoms in Rf is preferably 1 to 6.

Examples of the fluorine-containing monomer (2) include CH ₂ ═CFCF ₃ , CH ₂ ═CFCF ₂ CF ₃ , CH ₂ ═CFCF ₂ CF _{2 CF 3} , CHF═CHCF ₃ (1,3,3,3-tetrafluoropropene), CHF═CHCF ₃ (E form), CHF═CHCF ₃ (Z form ₎ , and _the like. Of these, 2,3,3,3 _- tetrafluoropropylene represented _{by CH 2 ═CFCF 3} is preferred.

In the manufacturing method disclosed herein, it is preferable to polymerize at least vinylidene fluoride or tetrafluoroethylene as the fluorine-containing monomer, since this can further suppress adhesion of the fluorine-containing elastomer to the polymerization tank, and it is more preferable to polymerize vinylidene fluoride.

In the manufacturing method of the present disclosure, a fluorine-free monomer may be polymerized together with the fluorine-containing monomer. Examples of the fluorine-free monomer include α-olefin monomers having 2 to 10 carbon atoms, such as ethylene, propylene, butene, and pentene; and alkyl vinyl ethers having an alkyl group having 1 to 20 carbon atoms, such as methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, cyclohexyl vinyl ether, hydroxybutyl vinyl ether, and butyl vinyl ether. These monomers and compounds may be used alone or in combination of two or more.

According to the production method of the present disclosure, an aqueous dispersion containing a fluorine-containing elastomer can be produced. The fluorine-containing elastomer obtained by the production method of the present disclosure contains a methylene group (-CH ₂ -) in the main chain. The fluorine-containing elastomer containing -CH ₂ - in the main chain is not particularly limited as long as it contains a chemical structure represented by -CH ₂ -, and examples thereof include fluorine-containing elastomers containing structures such as -CH ₂ -CF ₂ -, -CH ₂ -CH(CH ₃ )-, -CH ₂ -CH ₂ -, and -CH _{2 -CF 2} -(CF ₃ )-, which can be introduced into the main chain of the fluorine-containing elastomer by polymerizing, for example, vinylidene fluoride, propylene, ethylene, 2,3,3,3-tetrafluoropropylene, etc. The content of tetrafluoroethylene units in the fluorine-containing elastomer (the content of monomer units based on tetrafluoroethylene relative to the total monomer units of the fluorine-containing elastomer) may be less than 40 mol %.

As the fluorine-containing elastomer, a partially fluorinated elastomer is preferred because it can further suppress adhesion of the fluorine-containing elastomer to the polymerization tank while allowing the polymerization of the fluorine-containing monomer to proceed more smoothly. A partially fluorinated elastomer is a fluoropolymer that contains fluorine-containing monomer units, has a perfluoromonomer unit content of less than 90 mol% relative to the total monomer units, has a glass transition temperature of 20°C or less, and has a melting peak (ΔH) of 4.5 J/g or less.

The fluorine-containing elastomer preferably contains a monomer unit based on at least one monomer selected from the group consisting of tetrafluoroethylene (TFE), vinylidene fluoride (VdF), and a perfluoroethylenically unsaturated compound represented by the general formula: CF ₂ ═CF-Rf ^a (wherein Rf ^a is -CF ₃ or -ORf ^b (Rf ^b is a perfluoroalkyl group having 1 to 5 carbon atoms)) (e.g., hexafluoropropylene (HFP), perfluoro(alkyl vinyl ether) (PAVE), etc.). Of these, the fluorine-containing elastomer preferably contains a VdF unit or a TFE unit, and more preferably contains a VDF unit.

More specifically, examples of fluorine-containing elastomers include VdF-based fluorine-containing elastomers, TFE/propylene (Pr)-based fluorine-containing elastomers, TFE/Pr/VdF-based fluorine-containing elastomers, ethylene (Et)/HFP-based fluorine-containing elastomers, Et/HFP/VdF-based fluorine-containing elastomers, Et/HFP/TFE-based fluorine-containing elastomers, Et/TFE/PAVE-based fluorine-containing elastomers, etc. Among these, VdF-based fluorine-containing elastomers, TFE/Pr-based fluorine-containing elastomers, TFE/Pr/VdF-based fluorine-containing elastomers, and Et/TFE/PAVE-based fluorine-containing elastomers are more preferred in terms of good heat aging resistance and oil resistance.

The VdF-based fluorine-containing elastomer is a fluorine-containing elastomer having VdF units. The content of VdF units in the fluorine-containing elastomer is preferably 20 mol% or more, more preferably 40 mol% or more, even more preferably 50 mol% or more, and particularly preferably 60 mol% or more, based on the total monomer units. In the VdF-based fluorine-containing elastomer, the VdF units are preferably 20 mol% or more and 90 mol% or less of the total number of moles of VdF units and monomer units based on other monomers, more preferably 40 mol% or more and 85 mol% or less, even more preferably 45 mol% or more and 80 mol% or less, and particularly preferably 50 mol% or more and 80 mol% or less.

The other monomers in the VdF-based fluorine-containing elastomer are not particularly limited as long as they are monomers that can be copolymerized with VdF, and for example, the fluorine-containing monomers mentioned above can be used.

As the VdF-based fluorine-containing elastomer, at least one copolymer selected from the group consisting of VdF/HFP copolymer, VdF/TFE/HFP copolymer, VdF/CTFE copolymer, VdF/CTFE/TFE copolymer, VdF/PAVE copolymer, VdF/TFE/PAVE copolymer, VdF/HFP/PAVE copolymer, VdF/HFP/TFE/PAVE copolymer, VdF/TFE/Pr copolymer, VdF/Et/HFP copolymer, and VdF/fluorine-containing monomer (2) copolymer is preferred. In addition, it is more preferred that the other monomer than VdF is at least one monomer selected from the group consisting of TFE, HFP, and PAVE.

Among these, the VdF-based fluorine-containing elastomer is preferably at least one copolymer selected from the group consisting of VdF/HFP copolymer, VdF/TFE/HFP copolymer, VdF/fluorine-containing monomer (2) copolymer, VdF/PAVE copolymer, VdF/TFE/PAVE copolymer, VdF/HFP/PAVE copolymer, and VdF/HFP/TFE/PAVE copolymer, and more preferably at least one copolymer selected from the group consisting of VdF/HFP copolymer, VdF/HFP/TFE copolymer, VdF/fluorine-containing monomer (2) copolymer, and VdF/PAVE copolymer.

The VdF/PAVE copolymer preferably has a VdF/PAVE composition of (65 to 90)/(35 to 10) (mol %).
In addition, it is also one of the preferred embodiments that the VdF/PAVE composition is (50 to 78)/(50 to 22) (mol %).

As the VdF/TFE/PAVE copolymer, one having a VdF/TFE/PAVE composition of (40-80)/(3-40)/(15-35) (mol%) is preferred.

As the VdF/HFP/PAVE copolymer, one having a VdF/HFP/PAVE composition of (65-90)/(3-25)/(3-25) (mol%) is preferred.

As the VdF/HFP/TFE/PAVE copolymer, one having a VdF/HFP/TFE/PAVE composition of (40-90)/(0-25)/(0-40)/(3-35) (mol%) is preferred, and one having a VdF/HFP/TFE/PAVE composition of (40-80)/(3-25)/(3-40)/(3-25) (mol%) is more preferred.

As the copolymer of VdF/fluorine-containing monomer (2), the VdF/fluorine-containing monomer (2) units are preferably (85-20)/(15-80) (mol%), and other monomer units than VdF and the fluorine-containing monomer (2) are preferably 0-50 mol% of the total monomer units, and the molar percentage ratio of VdF/fluorine-containing monomer (2) units is more preferably (80-20)/(20-80). In addition, one preferred embodiment has a composition of VdF/fluorine-containing monomer (2) units of (78-50)/(22-50) (mol%).

Also preferred is a copolymer of VdF/fluorine-containing monomer (2) in which the VdF/fluorine-containing monomer (2) units are (85-50)/(15-50) (mol%) and the other monomer units other than VdF and fluorine-containing monomer (2) account for 1-50 mol% of the total monomer units. Preferred monomers other than VdF and fluorine-containing monomer (2) are the monomers exemplified as other monomers in VdF-based fluorine-containing elastomers, such as TFE, HFP, PMVE, perfluoroethyl vinyl ether (PEVE), PPVE, CTFE, trifluoroethylene, hexafluoroisobutene, vinyl fluoride, Et, Pr, alkyl vinyl ether, and monomers that provide crosslinkable groups, and among these, PMVE, CTFE, HFP, and TFE are more preferred.

TFE/Pr-based fluorine-containing elastomer refers to a fluorine-containing copolymer consisting of 45-70 mol% TFE and 55-30 mol% Pr. In addition to these two components, it may contain a specific third component.

The specific third component may include, for example, fluorine-containing monomers such as fluorine-containing olefins other than TFE (e.g., VdF, HFP, CTFE, perfluoro(butyl ethylene), etc.), fluorine-containing vinyl ethers (perfluoro(propyl vinyl ether), perfluoro(methyl vinyl ether), etc.); hydrocarbon monomers such as α-olefins (ethylene, 1-butene, etc.), vinyl ethers (ethyl vinyl ether, butyl vinyl ether, hydroxybutyl vinyl ether, etc.), and vinyl esters (vinyl acetate, vinyl benzoate, vinyl crotonate, vinyl methacrylate, etc.); and the like. The specific third component may be one type, or two or more types may be used in combination.

It is preferable that the TFE/Pr-based fluorine-containing elastomer contains VdF, and among TFE/Pr-based fluorine-containing elastomers, an elastomer consisting of TFE, Pr and VdF is called a TFE/Pr/VdF-based fluorine-containing elastomer.

The TFE/Pr/VdF-based fluorine-containing elastomer may further contain the specific third component other than VdF. The specific third component may be one type or a combination of two or more types. The total content of the third components in the TFE/Pr-based fluorine-containing elastomer is preferably 35 mol% or less, more preferably 33 mol% or less, and even more preferably 31 mol% or less.

As the Et/HFP copolymer, one having an Et/HFP composition of (35-80)/(65-20) (mol%) is preferred, and one having an Et/HFP composition of (40-75)/(60-25) (mol%) is more preferred.

The Et/HFP/TFE copolymer preferably has an Et/HFP/TFE composition of (35-75)/(25-50)/(0-15) (mol%), and more preferably has an Et/HFP/TFE composition of (45-75)/(25-45)/(0-10) (mol%).

The Et/TFE/PAVE copolymer preferably has a composition of Et/TFE/PAVE of (10-40)/(32-60)/(20-40) (mol%), more preferably (20-40)/(40-50)/(20-30) (mol%). PMVE is preferred as the PAVE.

As the fluorine-containing elastomer, a fluorine-containing elastomer containing VdF units is preferred, a VdF/HFP copolymer or a VdF/HFP/TFE copolymer is more preferred, and a VdF/HFP/TFE composition of (32-85)/(10-34)/(0-40) (mol%) is particularly preferred. The VdF/HFP/TFE composition is more preferably (32-85)/(15-34)/(0-34) (mol%), and even more preferably (47-81)/(17-32)/(0-26) (mol%).

For example, in the above VdF/HFP copolymer, the VdF/HFP composition is preferably (45-85)/(15-55) (mol%), more preferably (50-83)/(17-50) (mol%), even more preferably (55-81)/(19-45) (mol%), and particularly preferably (60-80)/(20-40) (mol%).

The above-mentioned structure is that of the main monomer of the fluorine-containing elastomer, and in addition to the main monomer, a monomer that provides a crosslinkable group may be copolymerized. The monomer that provides a crosslinkable group may be any monomer that can introduce an appropriate crosslinkable group into the fluorine-containing elastomer depending on the production method and crosslinking system, and examples of such monomers include known polymerizable compounds that include crosslinkable groups such as iodine atoms, bromine atoms, carbon-carbon double bonds, cyano groups, carboxyl groups, hydroxyl groups, amino groups, and ester groups.

Preferred examples of the monomer that provides a crosslinkable group include those represented by the general formula (3):
CY ¹ ₂ = CY ² R _f ² X ¹ (3)
(In the formula, Y ¹ and Y ² each represent a fluorine atom, a hydrogen atom or -CH ₃ ; R _f ² represents a linear or branched fluorine-containing alkylene group in which some or all of the hydrogen atoms have been substituted with fluorine atoms, which may have one or more ether-bonded oxygen atoms or an aromatic ring; and X ¹ represents an iodine atom or a bromine atom.)
Examples of the compound include those represented by the following formula:

Specific examples of the monomer that provides a crosslinkable group include those represented by the general formula (4):
CY ¹ ₂ = CY ² R _f ³ CHR ¹ -X ¹ (4)
(wherein Y ¹ , Y ² and X ¹ are the same as defined above, R _f ³ is a linear or branched fluorine-containing alkylene group which may have one or more ether-bonded oxygen atoms and in which some or all of the hydrogen atoms are substituted with fluorine atoms, i.e., a linear or branched fluorine-containing alkylene group in which some or all of the hydrogen atoms are substituted with fluorine atoms, a linear or branched fluorine-containing oxyalkylene group in which some or all of the hydrogen atoms are substituted with fluorine atoms, or a linear or branched fluorine-containing polyoxyalkylene group in which some or all of the hydrogen atoms are substituted with fluorine atoms; R ¹ is a hydrogen atom or a methyl group).
Iodine- or bromine-containing monomers represented by the general formulas (5) to (22):
CY ⁴ ₂ = CY ⁴ (CF ₂ ) _n −X ¹ (5)
(wherein Y ⁴ is the same or different and is a hydrogen atom or a fluorine atom, and n is an integer of 1 to 8).
CF ₂ =CFCF ₂ R _f ⁴ -X ¹ (6)
(In the formula, R ⁴ is -(OCF ₂ ) _n - or -(OCF(CF ₃ )) _n -, where n is an integer of 0 to 5.)
CF ₂ =CFCF ₂ (OCF(CF ₃ )CF ₂ ) _m (OCH ₂ CF ₂ CF ₂ ) _n OCH ₂ CF ₂ -X ¹ (7)
(In the formula, m is an integer from 0 to 5, and n is an integer from 0 to 5).
CF ₂ =CFCF ₂ (OCH ₂ CF ₂ CF ₂ ) _m (OCF(CF ₃ )CF ₂ ) _n OCF(CF ₃ )-X ¹ (8)
(In the formula, m is an integer from 0 to 5, and n is an integer from 0 to 5).
CF ₂ = CF (OCF ₂ CF (CF ₃ )) _m O (CF ₂ ) _n −X ¹ (9)
(wherein m is an integer from 0 to 5, and n is an integer from 1 to 8).
CF ₂ = CF (OCF ₂ CF (CF ₃ )) _m −X ¹ (10)
(wherein m is an integer from 1 to 5).
CF ₂ =CFOCF ₂ (CF(CF ₃ )OCF ₂ ) _n CF(-X ¹ )CF ₃ (11)
(wherein n is an integer from 1 to 4).
CF ₂ =CFO(CF ₂ ) _n OCF(CF ₃ )-X ¹ (12)
(wherein n is an integer from 2 to 5).
CF ₂ =CFO(CF ₂ ) _n -(C ₆ H ₄ )-X ¹ (13)
(wherein n is an integer from 1 to 6)
CF ₂ =CF(OCF ₂ CF(CF ₃ )) _n OCF ₂ CF(CF ₃ )−X ¹ (14)
(wherein n is an integer of 1 to 2).
CH ₂ =CFCF ₂ O(CF(CF ₃ )CF ₂ O) _n CF(CF ₃ )-X ¹ (15)
(wherein n is an integer from 0 to 5);
CF ₂ =CFO(CF ₂ CF(CF ₃ )O) _m (CF ₂ ) _n −X ¹ (16)
(In the formula, m is an integer of 0 to 5, and n is an integer of 1 to 3).
_CH2 = _CFCF2OCF ( _CF3 )OCF( _CF3 ) ^-X1 (17)
_CH2 = _{CFCF2OCH2CF2 - X1} ( ¹⁸ )
CF ₂ =CFO(CF ₂ CF (CF ₃ )O) _m CF ₂ CF (CF ₃ )-X ¹ (19)
(In the formula, m is an integer of 0 or more).
CF ₂ =CFOCF(CF ₃ )CF ₂ O(CF ₂ ) _n −X ¹ (20)
(In the formula, n is an integer of 1 or more).
CF ₂ =CFOCF ₂ OCF ₂ CF(CF ₃ )OCF ₂ -X ¹ (21)
CH ₂ =CH-(CF ₂ ) _n X ¹ (22)
(wherein n is an integer from 2 to 8).
(In the general formulas (5) to (22), ^X1 is the same as above.)
These may be used alone or in any combination.

（式中、ｍは１～５の整数であり、ｎは０～３の整数）
で表されるヨウ素含有フッ素化ビニルエーテルが好ましく挙げられ、より具体的には、

などが挙げられるが、これらの中でも、ＩＣＨ_２ＣＦ_２ＣＦ_２ＯＣＦ＝ＣＦ_２が好ましい。 The iodine- or bromine-containing monomer represented by the general formula (4) may be a monomer represented by the general formula (23):

(wherein m is an integer from 1 to 5, and n is an integer from 0 to 3).
Preferred examples of the iodine-containing fluorinated vinyl ethers include those represented by the following formula:

Among these, ICH ₂ CF ₂ CF _{2 OCF═CF2} is preferred.

More specifically, preferred examples of the iodine- or bromine-containing monomer represented by the general formula (5) include ICF ₂ CF ₂ CF═CH ₂ and I(CF ₂ CF ₂ ) ₂ CF═CH ₂ .

A more specific example of the iodine- or bromine-containing monomer represented by the general formula (9) is I(CF ₂ CF ₂ ) ₂ OCF═CF ₂ .

More specifically, preferred examples of the iodine- or bromine-containing monomer represented by the general formula (22) include CH ₂ ═CHCF ₂ CF ₂ I and I(CF ₂ CF ₂ ) ₂ CH═CH ₂ .

Also, the formula: R ² R ³ C═CR ⁴ -Z—CR ⁵ ═CR ⁶ R ⁷
(wherein R ² , R ³ , R ⁴ , R ⁵ , R ⁶ and R ⁷ are the same or different and all are H or an alkyl group having 1 to 5 carbon atoms; Z is a linear or branched alkylene or cycloalkylene group which may contain an oxygen atom and is preferably at least partially fluorinated having 1 to 18 carbon atoms, or a (per)fluoropolyoxyalkylene group) is also preferred as a monomer which provides a crosslinkable group. In the present disclosure, the term "(per)fluoropolyoxyalkylene group" means "fluoropolyoxyalkylene group or perfluoropolyoxyalkylene group".

Z is preferably a (per)fluoroalkylene group having 4 to 12 carbon atoms, and R ² , R ³ , R ⁴ , R ⁵ , R ⁶ and R ⁷ are preferably hydrogen atoms.

When Z is a (per)fluoropolyoxyalkylene group, the formula:
-(Q) _p -CF ₂ O-(CF ₂ CF ₂ O) _m -(CF ₂ O) _n -CF ₂ -(Q) _p -
(wherein Q is an alkylene group having 1 to 10 carbon atoms or an oxyalkylene group having 2 to 10 carbon atoms, p is 0 or 1, and m and n are integers such that the m/n ratio is 0.2 to 5 and the molecular weight of the (per)fluoropolyoxyalkylene group is in the range of 500 to 10,000, preferably 1,000 to 4,000.) In this formula, Q is preferably selected from -CH ₂ OCH ₂ - and -CH ₂ O(CH ₂ CH ₂ O) _s CH ₂ - (s = 1 to 3).

Preferred bis-olefins are
CH ₂ =CH-(CF ₂ ) ₂ -CH=CH ₂ ,
CH ₂ =CH-(CF ₂ ) ₄ -CH=CH ₂ ,
CH ₂ =CH-(CF ₂ ) ₆ -CH=CH ₂ ,
Formula: CH ₂ =CH-Z ¹ -CH=CH ₂
(In the formula, ^Z1 is -CH ₂ OCH ₂ -CF ₂ O-(CF ₂ CF ₂ O) _m -(CF ₂ O) _n -CF ₂ -CH ₂ OCH ₂ - (m/n is 0.5), and the molecular weight is preferably 2000.)
etc.

Of these, 3,3,4,4,5,5,6,6,7,7,8,8-dodecafluoro-1,9-decadiene, represented by CH ₂ ═CH--(CF ₂ ) ₆ -CH═CH ₂ , is preferred.

The number average molecular weight Mn of the fluorine-containing elastomer is preferably 1,000 to 1,000,000, more preferably 10,000 to 500,000, and particularly preferably 20,000 to 300,000.

The fluorine-containing elastomer preferably has a fluorine content of 50% by mass or more, more preferably 55% by mass or more, and even more preferably 60% by mass or more. The upper limit of the fluorine content is preferably 75% by mass or less, and more preferably 73% by mass or less. The fluorine content is calculated based on values measured by ¹⁹ F-NMR, ¹ H-NMR, elemental analysis, etc.

The fluorine-containing elastomer preferably has a Mooney viscosity at 100°C (ML1+10(100°C)) of 130 or less. The Mooney viscosity is more preferably 110 or less, and even more preferably 90 or less. The Mooney viscosity is more preferably 10 or more, and even more preferably 20 or more. Here, the Mooney viscosity is a value measured in accordance with JIS K 6300-1.2013.

The fluorine-containing elastomer preferably has a glass transition temperature of -50 to 0°C. The glass transition temperature is more preferably -2°C or lower, and even more preferably -3°C or lower. The glass transition temperature is more preferably -45°C or higher, and even more preferably -40°C or higher. The glass transition temperature may be -10°C or higher, or may be -9°C or higher. Here, the glass transition temperature can be determined from the DSC differential curve by heating 10 mg of a sample at 20°C/min using a differential scanning calorimeter (e.g., X-DSC7000 manufactured by Hitachi High-Tech Science Corporation) and calculating the glass transition temperature according to JIS K6240:2011.

The fluorine-containing elastomer preferably has an iodine content of 0.05 to 1.0% by mass. The iodine content is more preferably 0.08% by mass or more, even more preferably 0.10% by mass or more, and more preferably 0.80% by mass or less, even more preferably 0.60% by mass or less.

The iodine content can be determined by elemental analysis. Specifically, 5 mg of _Na2SO3 is mixed with 12 _mg of fluorine-containing elastomer, and 30 mg of a mixture _{of Na2CO3} and _K2CO3 in a 1: ₁ (mass ratio) is dissolved in 20 ml of pure water to prepare an absorption liquid, which is burned in oxygen in a quartz flask and left for 30 minutes, and then the iodine content can be measured using a Shimadzu 20A ion chromatograph. As the calibration curve, a KI standard solution, one containing 0.5 mass ppm of iodine ion, and one containing 1.0 mass ppm of iodine ion can be used.

The fluorine-containing elastomer preferably contains a —CH ₂ I structure. The presence of a —CH ₂ I structure can be confirmed by ¹ H-NMR spectrum. The fluorine-containing elastomer containing a —CH ₂ I structure can be obtained by iodine transfer polymerization.

In the fluorine-containing elastomer, the amount of -CH ₂ I structures relative to 100 mol % of -CH ₂ - structures is preferably 0.05 to 1.50 mol %. The amount of -CH ₂ I structures is more preferably 0.08 mol % or more, even more preferably 0.12 mol % or more, more preferably 1.20 mol % or less, even more preferably 1.00 mol % or less, and particularly preferably 0.80 mol % or less. The amount of -CH ₂ I structures can be determined by ¹ H-NMR spectrum.

The fluorine-containing elastomer more preferably contains a -CF ₂ CH ₂ I structure. The fluorine-containing elastomer containing a -CF ₂ CH ₂ I structure can be obtained by producing a VdF-based fluorine-containing elastomer by iodine transfer polymerization.

In the fluorine-containing elastomer, the amount of -CF ₂ CH ₂ I structure relative to 100 mol % of -CH ₂ - structure is preferably 0.05 to 1.50 mol %. The amount of -CF ₂ CH ₂ I structure is more preferably 0.08 mol % or more, even more preferably 0.12 mol % or more, more preferably 1.20 mol % or less, still more preferably 1.00 mol % or less, and particularly preferably 0.80 mol % or less. The amount of -CF ₂ CH ₂ I structure is calculated from the integral value A of all peak intensities observed in the region of chemical shift 3.75 to 4.05 ppm derived from -CH ₂ I in ¹ H-NMR spectrum and the integral value B of all peak intensities observed in the regions of chemical shift 2.3 to 2.7 ppm and 2.9 to 3.75 ppm derived from -CH ₂ - by A/B*100.

As the fluorine-containing monomer used in the manufacturing method of the present disclosure, any of the fluorine-containing monomers described for the fluorine-containing elastomers can be used as appropriate.

In the manufacturing method of the present disclosure, if at least one type of fluorine-containing compound (A) is used, it is possible to efficiently manufacture a fluorine-containing elastomer. In addition, in the manufacturing method of the present disclosure, two or more types of fluorine-containing compounds (A) may be used simultaneously, and other compounds having surface activity may be used simultaneously as long as they are volatile or may remain in molded articles containing the fluorine-containing elastomer.

The manufacturing method of the present disclosure preferably involves polymerizing a fluorine-containing monomer in the absence of a fluorine-containing surfactant that is substantially free of radically polymerizable unsaturated bonds (hereinafter sometimes simply referred to as a "fluorine-containing surfactant").

Conventionally, fluorine-containing surfactants have been used for the polymerization of fluorine-containing monomers, but the manufacturing method disclosed herein uses fluorine-containing compound (A), which makes it possible to polymerize fluorine-containing monomers and obtain fluorine-containing elastomers without using fluorine-containing surfactants.

In the present disclosure, "substantially in the absence of fluorine-containing surfactant" means that the content of fluorine-containing surfactant in the aqueous medium is 10 ppm by mass or less, and the content of fluorine-containing surfactant is preferably 1 ppm by mass or less, more preferably 100 ppb by mass or less, even more preferably 10 ppb by mass or less, and particularly preferably 1 ppb by mass or less.

Examples of the above-mentioned fluorine-containing surfactants include anionic fluorine-containing surfactants.

The anionic fluorine-containing surfactant may be, for example, a surfactant containing fluorine atoms having a total carbon number of 20 or less excluding the anionic group.

The above-mentioned fluorine-containing surfactant may also be a surfactant containing fluorine in which the molecular weight of the anionic portion is 1000 or less, preferably 800 or less.

The above "anionic portion" refers to the portion of the above fluorine-containing surfactant excluding the cation. For example, in the case of F(CF ₂ ) _n1 COOM represented by formula (I) described below, it is the portion "F(CF ₂ ) _n1 COO".

The above-mentioned fluorosurfactant also includes a fluorosurfactant having a LogPOW of 3.5 or less. The LogPOW is a partition coefficient between 1-octanol and water, and is expressed as LogP [wherein P represents the ratio of the fluorosurfactant concentration in octanol to the fluorosurfactant concentration in water when a 1:1 octanol/water mixture containing the fluorosurfactant undergoes phase separation].

The LogPOW is calculated from the HPLC elution time of the sample solution by performing HPLC on standard substances (heptanoic acid, octanoic acid, nonanoic acid, and decanoic acid) having known octanol/water partition coefficients under the following conditions: column: TOSOH ODS-120T column (φ4.6 mm×250 mm, manufactured by Tosoh Corporation), eluent: acetonitrile/ _0.6 % by mass HClO4/water=1/1 (vol/vol%), flow rate: 1.0 ml/min, sample amount: 300 μL, column temperature: 40° C., detection light: UV 210 nm, and creating a calibration curve between each elution time and the known octanol/water partition coefficient.

Specific examples of the above-mentioned fluorine-containing surfactants include those described in U.S. Patent Application Publication No. 2007/0015864, U.S. Patent Application Publication No. 2007/0015865, U.S. Patent Application Publication No. 2007/0015866, U.S. Patent Application Publication No. 2007/0276103, U.S. Patent Application Publication No. 2007/0117914, U.S. Patent Application Publication No. 2007/0142541, U.S. Patent Application Publication No. 2008/0015319, and U.S. Patent No. 3,250,808. , U.S. Pat. No. 3,271,341, JP 2003-119204 A, WO 2005/042593, WO 2008/060461, WO 2007/046377, JP 2007-119526 A, WO 2007/046482, WO 2007/046345, U.S. Patent Application Publication No. 2014/0228531, WO 2013/189824, and those described in WO 2013/189826.

The anionic fluorine-containing surfactant may be a compound represented by the following general formula (N ⁰ ):
X ⁿ⁰ - Rf ⁿ⁰ - Y ⁰ (N ⁰ )
(In the formula, X ⁿ⁰ is H, Cl or F. ^{Rf n0} is a linear, branched or cyclic alkylene group having 3 to 20 carbon atoms in which some or all of the H's are substituted with F, and the alkylene group may contain one or more ether bonds, and some of the H's may be substituted with Cl. Y ⁰ is an anionic group.

The anionic group of Y ⁰ may be -COOM, -SO ₂ M or -SO ₃ M, and may be -COOM or -SO ₃ M.

M is H, a metal atom, NR ⁷ ₄ , an imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent, and R ⁷ is --H or an organic group.

The above metal atoms include alkali metals (group 1), alkaline earth metals (group 2), etc., such as Na, K or Li.

R ⁷ may be -H or a C _1-10 organic group, may be -H or a C _1-4 organic group, or may be -H or a C _1-4 alkyl group.

M may be H, a metal atom or NR ⁷ ₄ , which may be H, an alkali metal (group 1), an alkaline earth metal (group 2) or NR ⁷ ₄ , which may be H, Na, K, Li or NH ₄ .

The above Rf ⁿ⁰ may be one in which 50% or more of H is substituted with fluorine.

（式中、Ｘ^ｎ２、Ｘ^ｎ３およびＸ^ｎ４は、同一若しくは異なってもよく、Ｈ、Ｆ、または、炭素数１～６のエーテル結合を含んでよい直鎖状または分岐鎖状の部分または完全フッ素化されたアルキル基である。Ｒｆ^ｎ５は、炭素数１～３のエーテル結合を含み得る直鎖状または分岐鎖状の部分または完全フッ素化されたアルキレン基であり、Ｌは連結基であり、Ｙ^０は、上記定義したものである。但し、Ｘ^ｎ２、Ｘ^ｎ３、Ｘ^ｎ４およびＲｆ^ｎ５の合計炭素数は１８以下である。）で表される化合物が挙げられる。 The compound represented by the above general formula (N ⁰ ) is
The following general formula (N ¹ ):
X ⁿ⁰ - (CF ₂ ) _m1 - Y ⁰ (N ¹ )
(wherein X ⁿ⁰ is H, Cl or F, m1 is an integer of 3 to 15, and Y ⁰ is as defined above), a compound represented by the following general formula (N ² ):
Rf ⁿ¹ -O-(CF(CF ₃ )CF ₂ O) _m2 CFX ⁿ¹ -Y ⁰ (N ² )
(wherein Rf ⁿ¹ is a perfluoroalkyl group having 1 to 5 carbon atoms, m2 is an integer of 0 to 3, X ⁿ¹ is F or CF ₃ , and Y ⁰ is as defined above), a compound represented by the following general formula (N ³ ):
Rf ⁿ² (CH ₂ ) _m3 - (Rf ⁿ³ ) _q - Y ⁰ (N ³ )
(wherein Rf ⁿ² is a partially or fully fluorinated alkyl group having 1 to 13 carbon atoms which may contain an ether bond and/or a chlorine atom, m3 is an integer from 1 to 3, Rf ⁿ³ is a linear or branched perfluoroalkylene group having 1 to 3 carbon atoms, q is 0 or 1, and Y ⁰ is as defined above), a compound represented by the following general formula (N ⁴ ):
Rf ⁿ⁴ -O-(CY ⁿ¹ Y ⁿ² ) _p CF ₂ -Y ⁰ (N ⁴ )
(wherein Rf ⁿ⁴ is a linear or branched partially or completely fluorinated alkyl group having 1 to 12 carbon atoms which may contain an ether bond, Y ⁿ¹ and Y ⁿ² are the same or different and are H or F, p is 0 or 1, and Y ⁰ is as defined above), and a compound represented by the following general formula (N ⁵ ):

(wherein X ⁿ² , X ⁿ³ and X ⁿ⁴ may be the same or different and are H, F, or a linear or branched moiety which may contain an ether bond or a fully fluorinated alkyl group having 1 to 6 carbon atoms; Rf ⁿ⁵ is a linear or branched moiety which may contain an ether bond or a fully fluorinated alkylene group having 1 to 3 carbon atoms; L is a linking group; and Y ⁰ is as defined above; provided that the total carbon number of X ⁿ² , X ⁿ³ , X ⁿ⁴ and Rf ⁿ⁵ is 18 or less).

More specifically, the compound represented by the general formula (N ⁰ ) includes perfluorocarboxylic acid (I) represented by the following general formula (I), ω-H perfluorocarboxylic acid (II) represented by the following general formula (II), perfluoroether carboxylic acid (III) represented by the following general formula (III), perfluoroalkyl alkylene carboxylic acid (IV) represented by the following general formula (IV), perfluoroalkoxy fluorocarboxylic acid (V) represented by the following general formula (V), perfluoroalkyl sulfonic acid (VI) represented by the following general formula (VII), ω-H perfluoro sulfonic acid (VII) represented by the following general formula (VII), perfluoroalkyl alkylene sulfonic acid (VIII) represented by the following general formula (VIII), alkyl alkylene carboxylic acid (IX) represented by the following general formula (IX), fluorocarboxylic acid (X) represented by the following general formula (X), alkoxy fluoro sulfonic acid (XI) represented by the following general formula (XI), compound (XII) represented by the following general formula (XII), compound (XIII) represented by the following general formula (XIII), and the like.

The perfluorocarboxylic acid (I) is represented by the following general formula (I):
F (CF ₂ ) _n1 COOM (I)
(wherein n1 is an integer of 3 to 14, M is H, a metal atom, NR ⁷ ₄ , an imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent, and R ⁷ is -H or an organic group.)

The ω-H perfluorocarboxylic acid (II) is represented by the following general formula (II):
H(CF ₂ ) _n2 COOM (II)
(wherein n2 is an integer from 4 to 15, and M is as defined above).

The perfluoroether carboxylic acid (III) is represented by the following general formula (III):
Rf ¹ -O-(CF(CF ₃ )CF ₂ O) _n3 CF(CF ₃ )COOM (III)
(wherein ^Rf1 is a perfluoroalkyl group having 1 to 5 carbon atoms, n3 is an integer of 0 to 3, and M is as defined above).

The perfluoroalkyl alkylene carboxylic acid (IV) is represented by the following general formula (IV):
Rf ² (CH ₂ ) _n4 Rf ³ COOM (IV)
(In the formula, Rf ² is a perfluoroalkyl group having 1 to 5 carbon atoms, Rf ³ is a linear or branched perfluoroalkylene group having 1 to 3 carbon atoms, n4 is an integer of 1 to 3, and M is as defined above.)

The alkoxyfluorocarboxylic acid (V) is represented by the following general formula (V):
Rf ⁴ -O-CY ¹ Y ² CF ₂ -COOM (V)
(wherein Rf ⁴ is a linear or branched partially or completely fluorinated alkyl group having 1 to 12 carbon atoms which may contain an ether bond and/or a chlorine atom, Y ¹ and Y ² are the same or different and are H or F, and M is as defined above).

The perfluoroalkylsulfonic acid (VI) is represented by the following general formula (VI):
F (CF ₂ ) _n5 SO ₃ M (VI)
(wherein n5 is an integer from 3 to 14, and M is as defined above).

The ω-H perfluorosulfonic acid (VII) is represented by the following general formula (VII):
H(CF ₂ ) _n6 SO ₃ M (VII)
(wherein n6 is an integer from 4 to 14, and M is as defined above).

The perfluoroalkyl alkylene sulfonic acid (VIII) is represented by the following general formula (VIII):
^Rf5 ( _CH2 ) _n7SO3M (VIII ₎
(wherein ^Rf5 is a perfluoroalkyl group having 1 to 13 carbon atoms, n7 is an integer of 1 to 3, and M is as defined above).

The alkyl alkylene carboxylic acid (IX) is represented by the following general formula (IX):
Rf ⁶ (CH ₂ ) _n8 COOM (IX)
(wherein ^Rf6 is a linear or branched partially or fully fluorinated alkyl group having 1 to 13 carbon atoms which may contain an ether bond, n8 is an integer from 1 to 3, and M is as defined above).

The fluorocarboxylic acid (X) is represented by the following general formula (X):
Rf ⁷ -O-Rf ⁸ -O-CF ₂ -COOM (X)
(wherein Rf ⁷ is a linear or branched, partially or fully fluorinated alkyl group having 1 to 6 carbon atoms which may contain an ether bond and/or a chlorine atom; Rf ⁸ is a linear or branched, partially or fully fluorinated alkyl group having 1 to 6 carbon atoms; and M is as defined above).

The alkoxyfluorosulfonic acid (XI) is represented by the following general formula (XI):
Rf ⁹ -O-CY ¹ Y ² CF ₂ -SO ₃ M (XI)
(In the formula, Rf ⁹ is a linear or branched alkyl group having 1 to 12 carbon atoms which may contain an ether bond and which is partially or completely fluorinated and may contain chlorine; Y ¹ and Y ² are the same or different and are H or F; and M is as defined above.)

（式中、Ｘ^１、Ｘ^２およびＸ^３は、同一若しくは異なってもよく、Ｈ、Ｆおよび炭素数１～６のエーテル結合を含み得る直鎖状または分岐鎖状の部分または完全フッ素化されたアルキル基であり、Ｒｆ^１０は、炭素数１～３のパーフルオロアルキレン基であり、Ｌは連結基であり、Ｙ^０はアニオン性基である。）で表されるものである。 The compound (XII) is represented by the following general formula (XII):

(wherein X ¹ , X ² and X ³ may be the same or different and are H, F and a linear or branched partially or completely fluorinated alkyl group having 1 to 6 carbon atoms which may contain an ether bond; Rf ¹⁰ is a perfluoroalkylene group having 1 to 3 carbon atoms; L is a linking group; and Y ⁰ is an anionic group).

Y ⁰ may be -COOM, -SO ₂ M or -SO ₃ M, and may be -SO ₃ M or -COOM, where M is as defined above.

Examples of L include single bonds and partially or fully fluorinated alkylene groups having 1 to 10 carbon atoms which may contain an ether bond.

The compound (XIII) is represented by the following general formula (XIII):
Rf ¹¹ -O-(CF ₂ CF(CF ₃ )O) _n9 (CF ₂ O) _n10 CF ₂ COOM (XIII)
(wherein ^Rf11 is a fluoroalkyl group containing chlorine and having 1 to 5 carbon atoms, n9 is an integer from 0 to 3, n10 is an integer from 0 to 3, and M is as defined above.) Examples of compound (XIII) include _CF2ClO ( _CF2CF ( _{CF3 )} O) _n9 ( _CF2O ) _n10CF2COONH4 (a mixture having an average molecular weight of ₇₅₀ , wherein n9 and n10 are as defined above).

The fluorine-containing surfactant may be one type of fluorine-containing surfactant or a mixture containing two or more types of fluorine-containing surfactants.

（各式中、Ｍは、Ｈ、金属原子、ＮＲ^７ _４、置換基を有していてもよいイミダゾリウム、置換基を有していてもよいピリジニウム又は置換基を有していてもよいホスホニウムである。Ｒ^７は、Ｈまたは有機基である。） The fluorine-containing surfactant may be a compound represented by the following formula: The fluorine-containing surfactant may be a mixture of these compounds. In one embodiment of the polymerization, the fluoromonomer is polymerized substantially in the absence of the compound represented by the following formula:
F( _CF2 ) ₇ COOM,
F(CF ₂ ) ₅ COOM,
H(CF ₂ ) ₆ COOM,
H(CF ₂ ) ₇ COOM,
_CF3O ( _CF2 ) _{3OCHFCF2COOM ,
C3F7OCF (CF3 ) CF2OCF} ( _CF3 )COOM,
CF ₃ CF ₂ CF ₂ OCF (CF ₃ )COOM,
CF ₃ CF ₂ OCF ₂ CF ₂ OCF ₂ COOM,
_{C2F5OCF (CF3 ) CF2OCF} ( _CF3 )COOM,
_CF3OCF ( _CF3 ) _CF2OCF ( _CF3 )COOM,
_{CF2ClCF2CF2OCF ( CF3 ) CF2OCF2COOM ,
CF2ClCF2CF2OCF2CF ( CF3 ) OCF2COOM ,
CF2ClCF} ( _CF3 )OCF( _CF3 ) _{CF2OCF2COOM ,
CF2ClCF} ( _CF3 ) _OCF2CF ( _CF3 ) _OCF2COOM ,

(In each formula, M is H, a metal atom, NR ⁷ ₄ , an imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent. R ⁷ is H or an organic group.)

According to the manufacturing method of the present disclosure, an aqueous dispersion of a fluorine-containing elastomer is obtained. The solids concentration (content of the fluorine-containing elastomer) of the obtained aqueous dispersion of the fluorine-containing elastomer is preferably 10 to 50% by mass, more preferably 15 to 40% by mass, and even more preferably 20 to 30% by mass at the time when the polymerization is completed.

The solids concentration (fluoroelastomer content) of a fluorine-containing elastomer aqueous dispersion can be determined by drying 1 g of the aqueous dispersion at 150°C for 180 minutes, measuring the mass of the heating residue, and calculating the ratio of the mass of the heating residue to the mass of the aqueous dispersion.

The aqueous dispersion of the fluorine-containing elastomer may contain fluorine-containing elastomer particles. The average particle size of the fluorine-containing elastomer particles is preferably 10 to 800 nm, more preferably 50 to 500 nm, and even more preferably 70 to 300 nm. The average particle size of the fluorine-containing elastomer particles is the cumulant average size, and can be measured by dynamic light scattering.

The number of fluorine-containing elastomer particles contained in the aqueous dispersion of fluorine-containing elastomer is preferably 1.0×10 ¹² particles/cc or more, more preferably 5.0×10 ¹² particles/cc or more, even more preferably 1.0×10 ¹³ particles/cc or more, particularly preferably 1.2×10 ¹⁴ particles/cc or more, and most preferably 1.3×10 ¹⁴ particles/cc or more. The above particle number (number of polymer particles) can be calculated according to the following formula.

The number of fluorine-containing elastomer particles obtained by the above formula is the number per 1 cc of water. The specific gravity is the specific gravity of the fluorine-containing elastomer. The specific gravity of the fluorine-containing elastomer can be determined in accordance with JIS Z 8807:2012.

The aqueous dispersion of the fluorine-containing elastomer may be subjected to treatments such as coagulation and heating.

The coagulation can be carried out by adding alkaline earth and earth metal salts to the aqueous dispersion. Examples of alkaline earth and earth metal salts include sulfates, nitrates, hydrochlorides, and acetates of calcium, magnesium, aluminum, etc.

The coagulated fluorine-containing elastomer may be washed with water to remove small amounts of impurities such as buffer solutions and salts present in the fluorine-containing elastomer, and then the washed fluorine-containing elastomer may be dried. The drying temperature is preferably 40 to 200°C, more preferably 60 to 180°C, and even more preferably 80 to 150°C.

The form of the fluorine-containing elastomer obtained after coagulation is not particularly limited, but may be gum, crumb, powder, pellets, etc., and is preferably gum or crumb. Gum is a small granular mass of fluorine-containing elastomer, and crumb is an amorphous mass of fluorine-containing elastomer that cannot maintain its small granular shape as a gum at room temperature and is fused to each other. Gum or crumb is preferably obtained by coagulating and drying the aqueous dispersion obtained by the manufacturing method disclosed herein using a conventionally known method.

A fluorine-containing elastomer composition can be produced by adding a crosslinking agent or the like to the aqueous dispersion of the fluorine-containing elastomer or the fluorine-containing elastomer obtained by the production method of the present disclosure. The type and amount of the crosslinking agent are not particularly limited, and can be used within the known range.

When the fluorine-containing elastomer is an uncrosslinked elastomer, the crosslinking system may be, for example, a peroxide crosslinking system, a polyol crosslinking system, a polyamine crosslinking system, etc., and is preferably at least one type selected from the group consisting of a peroxide crosslinking system and a polyol crosslinking system. From the viewpoint of chemical resistance, a peroxide crosslinking system is preferred, and from the viewpoint of heat resistance, a polyol crosslinking system is preferred.

Therefore, the crosslinking agent is preferably at least one crosslinking agent selected from the group consisting of polyol crosslinking agents and peroxide crosslinking agents, and more preferably a peroxide crosslinking agent.

The amount of crosslinking agent to be used may be selected appropriately depending on the type of crosslinking agent, etc., but is preferably 0.2 to 6.0 parts by mass, and more preferably 0.3 to 5.0 parts by mass, per 100 parts by mass of fluorine-containing elastomer.

Peroxide crosslinking can be carried out by using a peroxide-crosslinkable uncrosslinked elastomer as the fluorine-containing elastomer and an organic peroxide as the crosslinking agent.

The peroxide-crosslinkable uncrosslinked elastomer is not particularly limited, and may be an uncrosslinked elastomer having a peroxide-crosslinkable site. The peroxide-crosslinkable site is not particularly limited, and may be, for example, a site having an iodine atom, a site having a bromine atom, or the like.

The organic peroxide may be any organic peroxide that can easily generate peroxy radicals in the presence of heat or an oxidation-reduction system, such as 1,1-bis(t-butylperoxy)-3,5,5-trimethylcyclohexane, 2,5-dimethylhexane-2,5-dihydroperoxide, di-t-butyl peroxide, t-butylcumyl peroxide, dicumyl peroxide, α,α-bis(t-butylperoxy)-p-diisopropylbenzene, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)-hexyne-3, benzoyl peroxide, t-butylperoxybenzene, t-butylperoxymaleic acid, t-butylperoxyisopropylcarbonate, and t-butylperoxybenzoate. Among these, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane and 2,5-dimethyl-2,5-di(t-butylperoxy)-hexyne-3 are preferred.

The amount of organic peroxide is preferably 0.1 to 15 parts by mass, more preferably 0.3 to 5 parts by mass, per 100 parts by mass of fluorine-containing elastomer.

When the crosslinking agent is an organic peroxide, the fluorine-containing elastomer composition preferably further contains a crosslinking aid. Examples of crosslinking aids include triallyl cyanurate, triallyl isocyanurate (TAIC), triacrylformal, triallyl trimellitate, N,N'-m-phenylene bismaleimide, dipropargyl terephthalate, diallyl phthalate, tetraallyl terephthalate amide, triallyl phosphate, bismaleimide, fluorinated triallyl isocyanurate (1,3,5-tris(2,3,3-trifluoro-2-propenyl)-1,3,5-triazine-2,4,6-tetramethylphenyl)propanediol, and tetramethylphenyl ether. Examples of suitable amines include tris(diallylamine)-S-triazine, N,N-diallylacrylamide, 1,6-divinyldodecafluorohexane, hexaallylphosphoramide, N,N,N',N'-tetraallylphthalamide, N,N,N',N'-tetraallylmalonamide, trivinyl isocyanurate, 2,4,6-trivinylmethyltrisiloxane, tri(5-norbornene-2-methylene)cyanurate, triallyl phosphite, and trimethallyl isocyanurate. Among these, triallyl isocyanurate (TAIC) is preferred from the viewpoints of excellent crosslinkability, mechanical properties, and flexibility.

The amount of cross-linking aid is preferably 0.01 to 10 parts by mass, more preferably 0.01 to 7.0 parts by mass, and even more preferably 0.1 to 5.0 parts by mass, per 100 parts by mass of fluorine-containing elastomer. If the amount of cross-linking aid is less than 0.01 part by mass, the mechanical properties and flexibility will decrease. If the amount exceeds 10 parts by mass, the heat resistance will be poor and the durability of the molded product will also tend to decrease.

Polyol crosslinking can be carried out by using a polyol-crosslinkable uncrosslinked elastomer as the fluorine-containing elastomer and a polyhydroxy compound as the crosslinking agent. The amount of polyhydroxy compound in the polyol crosslinking system is preferably 0.01 to 10 parts by mass per 100 parts by mass of polyol-crosslinkable uncrosslinked elastomer. By using an amount of polyhydroxy compound in this range, polyol crosslinking can be sufficiently promoted. It is more preferably 0.02 to 8 parts by mass. Even more preferably 0.03 to 4 parts by mass.

The polyol-crosslinkable uncrosslinked elastomer is not particularly limited, and may be any uncrosslinked elastomer having a polyol-crosslinkable moiety. The polyol-crosslinkable moiety is not particularly limited, and may be, for example, a moiety having a vinylidene fluoride (VdF) unit. Methods for introducing the crosslinkable moiety include copolymerizing a monomer that provides a crosslinkable moiety during polymerization of the uncrosslinked elastomer.

As the polyhydroxy compound, polyhydroxy aromatic compounds are preferably used because of their excellent heat resistance.

The polyhydroxy aromatic compound is not particularly limited, and examples thereof include 2,2-bis(4-hydroxyphenyl)propane (hereinafter referred to as bisphenol A), 2,2-bis(4-hydroxyphenyl)perfluoropropane (hereinafter referred to as bisphenol AF. Bisphenol AF is available from, for example, Fujifilm Wako Pure Chemical Industries, Ltd., Central Glass Co., Ltd., etc.), 1,3-dihydroxybenzene, 1,7-dihydroxynaphthalene, 2,7-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 4,4'-dihydroxydiphenyl, 4,4'-dihydro Examples of the polyhydroxy aromatic compounds include hydroxystilbene, 2,6-dihydroxyanthracene, hydroquinone, catechol, 2,2-bis(4-hydroxyphenyl)butane (hereinafter referred to as bisphenol B), 4,4-bis(4-hydroxyphenyl)valeric acid, 2,2-bis(4-hydroxyphenyl)tetrafluorodichloropropane, 4,4'-dihydroxydiphenylsulfone, 4,4'-dihydroxydiphenylketone, tri(4-hydroxyphenyl)methane, 3,3',5,5'-tetrachlorobisphenol A, and 3,3',5,5'-tetrabromobisphenol A. These polyhydroxy aromatic compounds may be alkali metal salts, alkaline earth metal salts, etc., but when the copolymer is coagulated using an acid, it is preferable not to use the above metal salts. The amount of the polyhydroxy aromatic compound is 0.1 to 15 parts by mass, preferably 0.5 to 5 parts by mass, based on 100 parts by mass of the uncrosslinked elastomer.

When the crosslinking agent is a polyhydroxy compound, the fluorine-containing elastomer composition preferably further contains a crosslinking accelerator. The crosslinking accelerator promotes the formation of intramolecular double bonds in the defluorination reaction of the polymer main chain and the addition of the polyhydroxy compound to the double bonds thus formed.

The crosslinking accelerator may also be used in combination with an acid acceptor such as magnesium oxide or a crosslinking assistant.

Examples of crosslinking accelerators include onium compounds, and among onium compounds, at least one selected from the group consisting of ammonium compounds such as quaternary ammonium salts, phosphonium compounds such as quaternary phosphonium salts, oxonium compounds, sulfonium compounds, cyclic amines, and monofunctional amine compounds is preferred, and at least one selected from the group consisting of quaternary ammonium salts and quaternary phosphonium salts is more preferred.

The quaternary ammonium salt is not particularly limited, and examples thereof include 8-methyl-1,8-diazabicyclo[5,4,0]-7-undecenium chloride, 8-methyl-1,8-diazabicyclo[5,4,0]-7-undecenium iodide, 8-methyl-1,8-diazabicyclo[5,4,0]-7-undecenium hydroxide, 8-methyl-1,8-diazabicyclo[5,4,0]-7-undecenium methyl. ethyl sulfate, 8-ethyl-1,8-diazabicyclo[5,4,0]-7-undecenium bromide, 8-propyl-1,8-diazabicyclo[5,4,0]-7-undecenium bromide, 8-dodecyl-1,8-diazabicyclo[5,4,0]-7-undecenium chloride, 8-dodecyl-1,8-diazabicyclo[5,4,0]-7-undecenium hydroxide, 8-eicosyl-1,8-di Examples of the compound include azabicyclo[5,4,0]-7-undecenium chloride, 8-tetracosyl-1,8-diazabicyclo[5,4,0]-7-undecenium chloride, 8-benzyl-1,8-diazabicyclo[5,4,0]-7-undecenium chloride (hereinafter referred to as DBU-B. DBU-B can be obtained, for example, from Fujifilm Wako Pure Chemical Industries, Ltd.), 8-benzyl-1,8-diazabicyclo[5,4,0]-7-undecenium hydroxide, 8-phenethyl-1,8-diazabicyclo[5,4,0]-7-undecenium chloride, 8-(3-phenylpropyl)-1,8-diazabicyclo[5,4,0]-7-undecenium chloride, tetrabutylammonium hydrogen sulfate, tetrabutylammonium hydroxide, tetrabutylammonium chloride, and tetrabutylammonium bromide. Among these, DBU-B is preferred from the standpoints of crosslinkability, mechanical properties, and flexibility.

Furthermore, the quaternary phosphonium salt is not particularly limited, and examples thereof include tetrabutylphosphonium chloride, benzyltriphenylphosphonium chloride (hereinafter referred to as BTPPC), benzyltrimethylphosphonium chloride, benzyltributylphosphonium chloride, tributylallylphosphonium chloride, tributyl-2-methoxypropylphosphonium chloride, and benzylphenyl(dimethylamino)phosphonium chloride. Among these, benzyltriphenylphosphonium chloride (BTPPC) is preferred from the standpoints of crosslinkability, mechanical properties, and flexibility.

In addition, as a crosslinking accelerator, a solid solution of a quaternary ammonium salt and bisphenol AF, a solid solution of a quaternary phosphonium salt and bisphenol AF, or the chlorine-free crosslinking accelerator disclosed in JP-A-11-147891 can be used.

The amount of crosslinking accelerator is preferably 0.01 to 8.00 parts by mass, more preferably 0.02 to 5.00 parts by mass, and even more preferably 0.03 to 3.00 parts by mass, relative to 100 parts by mass of uncrosslinked elastomer. If the amount of crosslinking accelerator is less than 0.01 part by mass, crosslinking of the uncrosslinked elastomer may not proceed sufficiently, and the heat resistance, etc. of the obtained molded product may decrease. If the amount exceeds 8.00 parts by mass, there is a risk that the moldability of the fluorine-containing elastomer composition may decrease, and the elongation in mechanical properties and flexibility may also decrease.

The acid acceptor is used to neutralize acidic substances generated during polyol crosslinking, and specific examples include magnesium oxide, calcium hydroxide (e.g., NICC5000 (manufactured by Inoue Lime Industry Co., Ltd.), CALDIC#2000, CALDIC#1000 (manufactured by Omi Chemical Industry Co., Ltd.)), calcium oxide, litharge (lead oxide), zinc oxide, dibasic lead phosphite, hydrotalcite, etc., and it is preferable that the acid acceptor be at least one type selected from the group consisting of high activity magnesium oxide and low activity magnesium oxide.

Polyamine crosslinking can be carried out by using a polyamine-crosslinkable fluorine-containing elastomer as the fluorine-containing elastomer and a polyamine compound as the crosslinking agent.

The polyamine crosslinkable fluorine-containing elastomer is not particularly limited, and may be any fluorine-containing elastomer having a polyamine crosslinkable moiety. The polyamine crosslinkable moiety is not particularly limited, and may be, for example, a moiety having a vinylidene fluoride (VdF) unit. Methods for introducing the crosslinkable moiety include copolymerizing a monomer that provides a crosslinkable moiety during polymerization of the fluorine-containing elastomer.

Examples of polyamine compounds include hexamethylenediamine carbamate, N,N'-dicinnamylidene-1,6-hexamethylenediamine, 4,4'-bis(aminocyclohexyl)methane carbamate, etc. Among these, N,N'-dicinnamylidene-1,6-hexamethylenediamine is preferred.

There are no particular limitations on the method for obtaining the fluorine-containing elastomer composition, so long as it is a method that can uniformly mix the fluorine-containing elastomer obtained by the manufacturing method disclosed herein with the crosslinking agent. For example, there is a method in which a powder of the fluorine-containing elastomer coagulated alone is kneaded with other additives and compounding agents, if necessary, in a kneader such as an open roll.

The fluorine-containing elastomer composition may contain at least one type of polyfunctional compound. A polyfunctional compound is a compound having two or more functional groups of the same or different structures in one molecule. The functional group possessed by the polyfunctional compound may be any functional group that is generally known to be reactive, such as a carbonyl group, a carboxyl group, a haloformyl group, an amide group, an olefin group, an amino group, an isocyanate group, a hydroxyl group, or an epoxy group.

The fluorine-containing elastomer composition may contain various additives that are typically incorporated into elastomers, such as fillers (carbon black, barium sulfate, etc.), processing aids (wax, etc.), plasticizers, colorants, stabilizers, tackifiers (coumarone resin, coumarone-indene resin, etc.), release agents, electrical conductivity agents, thermal conductivity agents, surface non-tackifiers, flexibility agents, heat resistance improvers, flame retardants, etc., as well as one or more commonly used crosslinking agents and crosslinking accelerators different from those mentioned above.

The content of fillers such as carbon black is not particularly limited, but is preferably 0 to 300 parts by mass, more preferably 1 to 150 parts by mass, even more preferably 2 to 100 parts by mass, and particularly preferably 2 to 75 parts by mass, per 100 parts by mass of the fluorine-containing elastomer.

The content of processing aids such as wax is preferably 0 to 10 parts by mass, and more preferably 0 to 5 parts by mass, per 100 parts by mass of the fluorine-containing elastomer. The use of processing aids, plasticizers, and release agents tends to reduce the mechanical properties and sealing properties of the resulting molded product, so it is necessary to adjust the content of these agents within a range that allows for the desired properties of the resulting molded product.

A molded article can be obtained by crosslinking the fluorine-containing elastomer composition. A molded article can also be obtained by molding and crosslinking the fluorine-containing elastomer composition. The fluorine-containing elastomer composition can be molded by a conventionally known method. The molding and crosslinking methods and conditions may be within the range of known methods and conditions for the molding and crosslinking employed. The order of molding and crosslinking is not limited, and molding may be followed by crosslinking, crosslinking may be followed by molding, or molding and crosslinking may be performed simultaneously.

Examples of molding methods include, but are not limited to, compression molding, casting, injection molding, extrusion molding, and roto-cure molding. Examples of crosslinking methods that can be used include steam crosslinking, heat crosslinking, and radiation crosslinking, with steam crosslinking and heat crosslinking being preferred. Specific crosslinking conditions that are not limited to these are typically within a temperature range of 140 to 250°C and a crosslinking time of 1 minute to 24 hours, and can be appropriately determined depending on the types of crosslinking accelerator, crosslinking agent, and acid acceptor.

Furthermore, by heating the obtained molded product in an oven or the like, it is possible to improve the mechanical properties and the compression set properties at high temperatures. Specific crosslinking conditions, which are not limited, are usually in the temperature range of 140 to 300°C and in the range of 30 minutes to 72 hours, and can be appropriately determined depending on the types of crosslinking accelerator, crosslinking agent, acid acceptor, etc.

The obtained molded articles can be used as various parts in various fields such as the automotive industry, the aircraft industry, and the semiconductor industry. The molded articles can be used for applications similar to those of the crosslinked rubber molded articles described in JP 2013-216915 A and the fluororubber molded articles described in JP 2019-94430 A, such as sealing materials, sliding members, and non-adhesive members.

Examples of uses of the molded products include various sealing materials and packings such as rings, packings, gaskets, diaphragms, oil seals, and bearing seals. As a sealing material, it can be used in applications requiring excellent non-stickiness and low friction. It is particularly suitable for use as various sealing materials in the automotive industry, etc.

It can also be used as tubes, hoses, rolls, various rubber rolls, flexible joints, rubber sheets, coatings, belts, dampers, valves, valve seats, valve bodies, chemical-resistant coating materials, laminating materials, lining materials, etc.

Although an embodiment has been described above, it will be understood that various changes in form and details are possible without departing from the spirit and scope of the claims.

Next, we will explain the embodiments of the present disclosure using examples, but the present disclosure is not limited to these examples.

The numerical values in the examples were measured using the following methods.

Solids Concentration of Aqueous Dispersion 1 g of the aqueous dispersion was dried in a blower dryer at 150° C. for 180 minutes, the mass of the heating residue was measured, and the ratio (mass %) of the mass of the heating residue to the mass (1 g) of the aqueous dispersion was calculated.

Copolymer composition was determined by NMR analysis.

Polymer Adhesion Rate The ratio of the mass of polymer adhering to the polymerization vessel after the completion of polymerization to the total amount of polymer (fluoroelastomer) after the completion of polymerization (adhesion rate to the polymerization vessel) was calculated according to the following formula.
Polymer adhesion rate (mass %)=mass of polymer adhesion/mass of obtained polymer (including polymer adhesion)×100
Mass of obtained polymer = mass of aqueous dispersion x solids concentration (mass%) of aqueous dispersion / 100 + mass of polymer deposit The polymer deposit includes the polymer that adheres to the inside of the polymerization tank, such as the inner wall of the polymerization tank or the stirring blade, after the aqueous dispersion is extracted from the polymerization tank after the polymerization is completed, and the polymer that has been released from the aqueous dispersion by aggregation and is floating or settling without being dispersed in the aqueous dispersion. The mass of the polymer deposit is the mass after the moisture contained in the polymer deposit is removed by drying at 120°C.

Particle number (number of fluorine-containing elastomer particles in aqueous dispersion)
Calculated using the following formula.

In the formula, the average particle size is the average particle size (cumulant average size) of the fluorine-containing elastomer particles in the aqueous dispersion, and is measured by dynamic light scattering using an ELSZ-1000S (manufactured by Otsuka Electronics Co., Ltd.) and calculated by the cumulant method.
In the formula, the number of polymer particles (number of fluorine-containing elastomer particles) is the number per cc of water, and the specific gravity of all the fluorine-containing elastomers in the examples and comparative examples was set to 1.8.

Mooney Viscosity (ML1+10 (100°C))
The Mooney viscosity was measured using a Mooney viscometer MV2000E manufactured by ALPHA TECHNOLOGIES at 100° C. in accordance with JIS K 6300-1.2013.

Maximum torque level (MH)
For the fluorine-containing elastomer compositions prepared in the Examples and Comparative Examples, crosslinking curves were determined during crosslinking at 160° C. using a rubber vulcanization tester MDRH2030 (manufactured by M&K Co., Ltd.), and maximum torque levels (MH) were determined.

Compression set (CS)
In accordance with JIS K6262, the compression set of the O-rings produced in the examples and comparative examples was measured under conditions of 200° C., 72 hours, and a compression ratio of 25%.

Example 1
(Production of Fluorine-Containing Elastomer Aqueous Dispersion)
In a 3L stainless steel polymerization tank, 1500g of deionized water and 1.50g of a 10% by mass aqueous solution of _CH2 = _CFCF2OCF ( _CF3 ) _COONH4 (compound (a1)) were added, the polymerization tank was sealed, and the system was replaced with nitrogen to remove oxygen. The polymerization tank was heated to 80°C, and VdF, TFE and HFP (initial monomer) were injected with stirring in a molar ratio of vinylidene fluoride [VdF]/tetrafluoroethylene [TFE]/hexafluoropropylene [HFP] (=19/11/70 mol%) so that the internal pressure of the polymerization tank was 1.47 MPaG.

Next, an aqueous solution of polymerization initiator, in which 0.026 g of ammonium persulfate (APS) was dissolved in deionized water, was injected with nitrogen gas to initiate polymerization. As the polymerization progressed, when the internal pressure dropped to 1.45 MPaG, a mixed monomer of VDF/TFE/HFP (=50/20/30 mol%) was charged so that the internal pressure remained constant at 1.47 MPaG.

When 14 g of the mixed monomer was added, 2.19 g of the diiodine compound I(CF ₂ ) ₄ I was injected with nitrogen gas.

3.0 hours after the start of polymerization, an aqueous solution of polymerization initiator (0.026 g of APS) was injected with nitrogen gas.

Immediately after the diiodine compound I(CF ₂ ) ₄ I was injected until 70% of the total amount of the mixed monomers was supplied, a total of 3.00 g of a 10% by mass aqueous solution of CH ₂ ═CFCF ₂ OCF(CF ₃ )COONH ₄ (compound (a1)) was intermittently supplied to the polymerization tank.

5.30 hours after the start of polymerization, stirring was stopped and the polymerization tank was depressurized until it reached atmospheric pressure, thereby terminating the polymerization.

The polymerization tank was cooled to obtain an aqueous dispersion of a fluorine-containing elastomer. The solids concentration, polymer adhesion rate, and particle number of the aqueous dispersion are shown in Table 1.

An aqueous aluminum sulfate solution was added to the resulting fluorine-containing elastomer aqueous dispersion to cause coagulation. The resulting coagulate was washed with water and dried to obtain a fluorine-containing elastomer. The copolymer composition was examined by NMR analysis and found to be VdF/TFE/HFP = 50/20/30 (mol%). The Mooney viscosity of the fluorine-containing elastomer is shown in Table 1.

Example 2
(Production of Fluorine-Containing Elastomer Aqueous Dispersion)
In a 3L stainless steel polymerization tank, 1500g of deionized water and 0.93g of a 10% by mass aqueous solution of _CH2 = _CFCF2OCF ( _CF3 ) _COONH4 (compound (a1)) were added, the polymerization tank was sealed, and the system was replaced with nitrogen to remove oxygen. The polymerization tank was heated to 80°C, and VdF, TFE and HFP (initial monomer) were injected with stirring in a molar ratio of vinylidene fluoride [VdF]/tetrafluoroethylene [TFE]/hexafluoropropylene [HFP] (=19/11/70 mol%) so that the internal pressure of the polymerization tank was 1.47 MPaG.

Next, an aqueous solution of polymerization initiator, in which 0.026 g of ammonium persulfate (APS) was dissolved in deionized water, was injected with nitrogen gas to initiate polymerization. As the polymerization progressed, when the internal pressure dropped to 1.45 MPaG, a mixed monomer of VDF/TFE/HFP (=50/20/30 mol%) was charged so that the internal pressure remained constant at 1.47 MPaG.

When 14 g of the mixed monomer was added, 2.19 g of the diiodine compound I(CF ₂ ) ₄ I was injected with nitrogen gas.

3.0 hours and 6.0 hours after the start of polymerization, an aqueous solution of polymerization initiator (0.026 g of APS) was injected with nitrogen gas.

Immediately after the diiodine compound I(CF ₂ ) ₄ I was injected until 70% of the total amount of the mixed monomer was supplied, a total of 2.81 g of a 10% by mass aqueous solution of CH ₂ ═CFCF ₂ OCF(CF ₃ )COONH ₄ (compound (a1)) was intermittently supplied to the polymerization tank.

6.32 hours after the start of polymerization, stirring was stopped and the polymerization tank was depressurized until it reached atmospheric pressure, thereby terminating the polymerization.

The polymerization tank was cooled to obtain an aqueous dispersion of a fluorine-containing elastomer. The solids concentration, polymer adhesion rate, and particle number of the aqueous dispersion are shown in Table 1.

An aqueous aluminum sulfate solution was added to the resulting fluorine-containing elastomer aqueous dispersion to cause coagulation. The resulting coagulate was washed with water and dried to obtain a fluorine-containing elastomer. The copolymer composition was examined by NMR analysis and found to be VdF/TFE/HFP = 50/20/30 (mol%). The Mooney viscosity of the fluorine-containing elastomer is shown in Table 1.

Example 3
(Production of Fluorine-Containing Elastomer Aqueous Dispersion)
In a 3L stainless steel polymerization tank, 1500g of deionized water and 0.93g of a 10% by mass aqueous solution of _CH2 = _CFCF2OCF ( _CF3 ) _COONH4 (compound (a1)) were added, the polymerization tank was sealed, and the system was replaced with nitrogen to remove oxygen. The polymerization tank was heated to 80°C, and VdF, TFE and HFP (initial monomer) were injected with stirring in a molar ratio of vinylidene fluoride [VdF]/tetrafluoroethylene [TFE]/hexafluoropropylene [HFP] (=19/11/70 mol%) so that the internal pressure of the polymerization tank was 1.47 MPaG.

Next, an aqueous solution of polymerization initiator, in which 0.026 g of ammonium persulfate (APS) was dissolved in deionized water, was injected with nitrogen gas to initiate polymerization. As the polymerization progressed, when the internal pressure dropped to 1.45 MPaG, a mixed monomer of VDF/TFE/HFP (=50/20/30 mol%) was charged so that the internal pressure remained constant at 1.47 MPaG.

When 14 g of the mixed monomer was added, 2.19 g of the diiodine compound I(CF ₂ ) ₄ I was injected with nitrogen gas.

3.0 hours after the start of polymerization, an aqueous solution of polymerization initiator (0.026 g of APS) was injected with nitrogen gas.

Immediately after the diiodine compound I (CF ₂ ) ₄ I was injected until 70% of the total amount of the mixed monomer was fed, a total of 3.00 g of a 10% by mass aqueous solution of CF ₂ ═CFOCF ₂ CF ₂ COONH ₄ (compound (a2)) was intermittently fed to the polymerization tank.

5.72 hours after the start of polymerization, stirring was stopped and the polymerization tank was depressurized until it reached atmospheric pressure, thereby terminating the polymerization.

The polymerization tank was cooled to obtain an aqueous dispersion of a fluorine-containing elastomer. The solids concentration, polymer adhesion rate, and particle number of the aqueous dispersion are shown in Table 1.

An aqueous aluminum sulfate solution was added to the resulting fluorine-containing elastomer aqueous dispersion to cause coagulation. The resulting coagulate was washed with water and dried to obtain a fluorine-containing elastomer. The copolymer composition was examined by NMR analysis and found to be VdF/TFE/HFP = 50/20/30 (mol%). The Mooney viscosity of the fluorine-containing elastomer is shown in Table 1.

Example 4
(Production of Fluorine-Containing Elastomer Aqueous Dispersion)
In a 3L stainless steel polymerization tank, 1500g of deionized water and 0.93g of a 10% by mass aqueous solution of _CH2 = _CFCF2OCF ( _CF3 ) _COONH4 (compound (a1)) were added, the polymerization tank was sealed, and the system was replaced with nitrogen to remove oxygen. The polymerization tank was heated to 80°C, and VdF, TFE and HFP (initial monomer) were injected with stirring in a molar ratio of vinylidene fluoride [VdF]/tetrafluoroethylene [TFE]/hexafluoropropylene [HFP] (=19/11/70 mol%) so that the internal pressure of the polymerization tank was 1.47 MPaG.

Next, an aqueous solution of polymerization initiator, in which 0.026 g of ammonium persulfate (APS) was dissolved in deionized water, was injected with nitrogen gas to initiate polymerization. As the polymerization progressed, when the internal pressure dropped to 1.45 MPaG, a mixed monomer of VDF/TFE/HFP (=50/20/30 mol%) was charged so that the internal pressure remained constant at 1.47 MPaG.

When 14 g of the mixed monomer was added, 2.19 g of the diiodine compound I(CF ₂ ) ₄ I was injected with nitrogen gas.

3.0 hours after the start of polymerization, an aqueous solution of polymerization initiator (0.026 g of APS) was injected with nitrogen gas.

Immediately after the diiodine compound I (CF ₂ ) ₄ I was injected until 70% of the total amount of the mixed monomer was supplied, a total of 3.00 g of a 10% by mass aqueous solution of CF ₂ ═CFOCF ₂ CF ₂ SO ₃ Na (compound (a3)) was intermittently supplied to the polymerization tank.

5.82 hours after the start of polymerization, stirring was stopped and the polymerization tank was depressurized until it reached atmospheric pressure, thereby terminating the polymerization.

The polymerization tank was cooled to obtain an aqueous dispersion of a fluorine-containing elastomer. The solids concentration, polymer adhesion rate, and particle number of the aqueous dispersion are shown in Table 1.

An aqueous aluminum sulfate solution was added to the resulting fluorine-containing elastomer aqueous dispersion to cause coagulation. The resulting coagulate was washed with water and dried to obtain a fluorine-containing elastomer. The copolymer composition was examined by NMR analysis and found to be VdF/TFE/HFP = 50/20/30 (mol%). The Mooney viscosity of the fluorine-containing elastomer is shown in Table 1.

Comparative Example 1
(Production of Fluorine-Containing Elastomer Aqueous Dispersion)
In a 3L stainless steel polymerization tank, 1500g of deionized water and 3.00g of a 5% by mass aqueous solution of _CH2 = _CFCF2OCF ( _CF3 ) _CF2OCF ( _CF3 ) _COONH4 (compound (b)) were added, the polymerization tank was sealed, and the system was replaced with nitrogen to remove oxygen. The polymerization tank was heated to 80°C, and VdF, TFE and HFP (initial monomer) were injected with stirring in a molar ratio of vinylidene fluoride [VdF]/tetrafluoroethylene [TFE]/hexafluoropropylene [HFP] (=19/11/70 mol%) so that the internal pressure of the polymerization tank was 1.47 MPaG.

Next, an aqueous solution of polymerization initiator, in which 0.026 g of ammonium persulfate (APS) was dissolved in deionized water, was injected with nitrogen gas to initiate polymerization. As the polymerization progressed, when the internal pressure dropped to 1.45 MPaG, a mixed monomer of VDF/TFE/HFP (=50/20/30 mol%) was charged so that the internal pressure remained constant at 1.47 MPaG.

When 14 g of the mixed monomer was added, 2.19 g of the diiodine compound I(CF ₂ ) ₄ I was injected with nitrogen gas.

3.0 hours and 6.0 hours after the start of polymerization, an aqueous solution of polymerization initiator (0.026 g of APS) was injected with nitrogen gas.

Immediately after the diiodine compound I( _CF2 ) _4I was injected until 70% of the total amount of the mixed monomers was supplied, a total of 6.00 g of a 5 mass% aqueous solution of _CH2 = _CFCF2OCF ( _CF3 ) _CF2OCF ( _CF3 ) _COONH4 (compound (b)) was intermittently supplied to the polymerization tank.

6.93 hours after the start of polymerization, stirring was stopped and the polymerization tank was depressurized until it reached atmospheric pressure, thereby terminating the polymerization.

The polymerization tank was cooled to obtain an aqueous dispersion of a fluorine-containing elastomer. The solids concentration, polymer adhesion rate, and particle number of the aqueous dispersion are shown in Table 1.

An aqueous aluminum sulfate solution was added to the resulting fluorine-containing elastomer aqueous dispersion to cause coagulation. The resulting coagulate was washed with water and dried to obtain a fluorine-containing elastomer. The copolymer composition was examined by NMR analysis and found to be VdF/TFE/HFP = 50/20/30 (mol%). The Mooney viscosity of the fluorine-containing elastomer is shown in Table 1.

Comparative Example 2
(Production of Fluorine-Containing Elastomer Aqueous Dispersion)
In a 3L stainless steel polymerization tank, 1500g of deionized water and 0.93g of a 10% by mass aqueous solution of _CH2 = _CFCF2OCF ( _CF3 ) _COONH4 (compound (a1)) were added, the polymerization tank was sealed, and the system was replaced with nitrogen to remove oxygen. The polymerization tank was heated to 80°C, and VdF, TFE and HFP (initial monomer) were injected with stirring in a molar ratio of vinylidene fluoride [VdF]/tetrafluoroethylene [TFE]/hexafluoropropylene [HFP] (=19/11/70 mol%) so that the internal pressure of the polymerization tank was 1.47 MPaG.

Next, an aqueous solution of polymerization initiator, in which 0.026 g of ammonium persulfate (APS) was dissolved in deionized water, was injected with nitrogen gas to initiate polymerization. As the polymerization progressed, when the internal pressure dropped to 1.45 MPaG, a mixed monomer of VDF/TFE/HFP (=50/20/30 mol%) was charged so that the internal pressure remained constant at 1.47 MPaG.

When 14 g of the mixed monomer was added, 2.19 g of the diiodine compound I(CF ₂ ) ₄ I was injected with nitrogen gas.

3.0 hours after the start of polymerization, an aqueous solution of polymerization initiator (0.026 g of APS) was injected with nitrogen gas.

5.52 hours after the start of polymerization, stirring was stopped and the polymerization tank was depressurized until it reached atmospheric pressure, thereby terminating the polymerization.

The polymerization tank was cooled to obtain an aqueous dispersion of a fluorine-containing elastomer. The solids concentration, polymer adhesion rate, and particle number of the aqueous dispersion are shown in Table 1.

An aqueous aluminum sulfate solution was added to the resulting fluorine-containing elastomer aqueous dispersion to cause coagulation. The resulting coagulate was washed with water and dried to obtain a fluorine-containing elastomer. The copolymer composition was examined by NMR analysis and found to be VdF/TFE/HFP = 50/20/30 (mol%). The Mooney viscosity of the fluorine-containing elastomer is shown in Table 1.

(Preparation of O-ring)
100 parts by mass of the fluorine-containing elastomer obtained in the above Examples and Comparative Examples, 20 parts by mass of carbon black (MT Carbon, Thermax N-990, manufactured by Cancarb), 4 parts by mass of triallyl isocyanurate (TAIC, manufactured by Nippon Kasei Chemical Industry Co., Ltd.), and 1.5 parts by mass of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane (Perhexa 25B, manufactured by NOF Corporation) were kneaded using an open roll to prepare a fluorine-containing elastomer composition. The maximum torque level (MH) of the fluorine-containing elastomer composition is shown in Table 1.

The obtained fluorine-containing elastomer composition was press-crosslinked at 160°C for 10 minutes and oven-crosslinked at 180°C for 4 hours to produce an O-ring (P24 size). The compression set (CS) of the O-ring is shown in Table 1.

Claims (8)

A method for producing an aqueous dispersion of a fluorine-containing elastomer, comprising polymerizing a fluorine-containing monomer in the presence of an aqueous medium and a fluorine-containing compound (A) to produce an aqueous dispersion containing a fluorine-containing elastomer, comprising the steps of:
the fluorine-containing elastomer contains a methylene group in its main chain,
The fluorine-containing compound (A) is represented by the general formula (A):
CX ⁱ X ^k =CX ^j R ^a -(CZ ¹ Z ² ) _k -Y ³ (A)
(wherein, X ⁱ , X ^j and X ^k are the same or different and are F, Cl, H or CF ₃ ; Y ³ is a hydrophilic group , which is -NH ₂ , -P(O)(OM) ₂ , -OP(O)(OM) ₂ , -SO ₃ M, -OSO ₃ M or -COOM (in each formula, M is H, a metal atom, NR ⁷ ₄ , an imidazolium which may have a substituent, a pyridinium which may have a substituent or a phosphonium which may have a substituent, R ⁷ is H or an organic group, which may be the same or different, and any two of the four R ⁷ in NR ⁷ ₄ may be bonded to each other to form a ring) ; R ^a is -(C═O)-, -(C═O)-O- or a hydrocarbon group which may contain an ether bond and in which some or all of the hydrogen atoms bonded to the carbon atoms may be substituted with fluorine ; Z ^Z1 and ^Z2 are the same or different and are H, F or _CF3 ; k is 0 or 1. However, at least one of Xi, ^Xk , ^Xj , ^Ra , ^{Z1 and Z2} contains F. The number of carbon atoms in the portion excluding the hydrophilic group is 6 or less.
The production method, comprising supplying a fluorine-containing compound (A) after initiating polymerization of the fluorine-containing monomer. The process according to claim 1 , wherein the fluorine-containing elastomer contains vinylidene fluoride units. The method according to claim 1 or 2, wherein the fluorine-containing elastomer contains 50 mol% or more of vinylidene fluoride units relative to the total monomer units. The method according to claim 1 or 2, in which the fluorine-containing compound (A) is supplied even before the polymerization of the fluorine-containing monomer begins. The method according to claim 1 or 2, wherein the amount of fluorine-containing compound (A) supplied after the polymerization of the fluorine-containing monomer is started is 30 to 300 ppm by mass relative to the aqueous medium. 3. The process according to claim 1 , wherein the fluorine-containing monomer is polymerized in an aqueous medium containing a fluorine-containing surfactant having no radically polymerizable unsaturated bond in an amount of 10 ppm by mass or less. The method according to claim 1 or 2, wherein the Mooney viscosity (ML1+10 (100°C)) of the fluorine-containing elastomer is 10 to 130. The fluorine-containing compound (A) is represented by the general formula (A1):
CX ⁱ X ^k =CX ^j -OR-(CZ ¹ Z ² ) _k -Y ³
(wherein Xi, ^Xj , ^Xk , ^Z1 , ^Z2 , k ^{and Y3} are as defined above, and R is a fluorinated alkylene group or a fluorinated oxyalkylene group having 1 to 3 carbon atoms), and a compound represented by general formula (A2):
CX ⁱ X ^k =CX ^j -CZ ¹ Z ² -O-R-(CZ ¹ Z ² ) _k -Y ³
(wherein Xi, ^Xj , ^Xk , ^Z1 , ^Z2 , k ^{and Y3} are as defined above, and R is a fluorinated alkylene group or a fluorinated oxyalkylene group having 1 or 2 carbon atoms).